I always wondered if anything could bring me out of lurking, but here we are! This post is gigantic (~2000 words), so feel free to tl;dr it, but if you want to read, let's roll!
To me the greatest thing about Crusaders of the Lost Mark is the unspoken undercurrent that
almost every song has a double meaning--and, more than that, the hidden meaning is either equally important or
more important than the surface meaning.
Let's start with the way that Diamond Tiara and the CMCs think they're singing about themselves, but are actually singing just as much about each other. Without a single explicit line of dialogue to this effect, this isn't merely a Diamond Tiara redemption episode and CMC cutie mark episode, but also a recap episode where Diamond Tiara is re-enacting or reminding us of almost every key moment of the CMCs' development. You see,
Diamond Tiara and the Cutie Mark Crusaders have parallel story arcs. Bear with me while I explain!
Personally, I've always loved Diamond Tiara because I watch the show for entertainment without trying to relate or project myself into situations or whatever else people do when watching entertainment. Last season I had her as my 12th favorite character and 11th favorite pony (Discord was up there), beating out half the mane six and Princess Celestia, among others. But I know that's unusual because I watch several blind commentators. I've watched Diamond Tiara get all the worst verbal abuse and then I've watched these commentators immediately turn around on her for this episode. On a surface level, they might say it's sudden and they might even feel conflicted. But what's going on here subconsciously?
As nice as the metaphors at the beginning of The Pony I Want To Be are, let's think about the chorus:

Would you believe that I've always wished I could be somepony else
Yet I can't see what I need to do to be the pony I want to be
The answer is yes, we
would believe that she's always wished she could be somepony else. But why do we believe it so quickly? Because (here's the bombshell)
for five seasons the Cutie Mark Crusaders have wished they could be somepony else! They, too, can't see what they need to do to be the ponies they want to be. Obviously part of that is chasing after every talent in the world to try and figure out who they are, but I'm also talking about moments like this:

Scootaloo: But flying's what pegasus ponies are supposed to do! You flew when you carried the flag in the games!
Rainbow Dash: But that was me! You're you!
And I'm talking about moments like this:

Sweetie Belle: I decided to make a grand entrance. I made myself all beautiful, just like my big sister.
While there are still viewers who consider this episode rushed (and I'm not one of them), I've noticed that there aren't nearly as many as there were for Magical Mystery Cure. I really believe that's because Diamond Tiara's introspection is the same general flavor of introspection that the CMCs have been going through. The episode didn't
need much time to establish her inner journey because we've already been following something similar for five seasons!
How about the chase song? I'll talk about two sequences from it, but let's start with this one...

We know you want friends who admire you
You want to be the star with all the power too
Has Diamond Tiara been the only one to fall into that trap before? Nope!


We could be the big shots around here!
[cut to the CMCs fantasizing about showing off and being stars]
No wonder they so easily sympathize with her: they've been there before with all the events of Twilight Time--and even earlier in Ponyville Confidential, for that matter! Remember, while Diamond Tiara pushed them to keep going with the gossip column, they kicked off the idea themselves.
Now let's look at an even more interesting aspect to the chase song...

Stop! This is not the answer
Wait! And it's plainly seen
Listen! You can redeem yourself, but by helping others, not by being mean
Other than the very last part about being mean (though in One Bad Apple they even had their brief stint of carefully-plotted revenge), what words have been aimed at the CMCs more often than these?
"
Stop! This is not the answer" - How many "wrong" answers have the CMCs come up with? Although they weren't
morally wrong, they've explored every
incorrect avenue to get their cutie marks--as we just saw at the beginning of the episode.
"
Wait! And it's plainly seen" - Who else has plainly seen that the CMCs were pursuing the wrong ideas? Twilight and Rainbow Dash, probably among others I'm forgetting:


"
Listen! You can redeem yourself, but by helping others..." - What did the CMCs need to do to get their cutie marks? They needed to
help others! They're essentially singing to themselves with this part and again in this later bit:
You can stop right now and try another start
Finally free yourself from the dark
And see the light
And see the light of your cutie mark
It's easy to get caught up in all the prior characterization that has painted the CMCs as "good" and Diamond Tiara as "evil," but an overlooked aspect of their development is that both have been operating from self-centered perspectives (albeit with different motives).
Diamond Tiara can only come to understand her cutie mark when she stops focusing on what it does for her and what she can do for others; the CMCs can only earn their cutie marks in the first place when
they stop focusing on themselves and look toward what they can do for others. They both had to "stop right now and try another start" to see the light of their cutie marks.
This is what I'm talking about when I say they've been on parallel paths!
Now... How about this song toward the end?

There's so much I can do to help everypony else
I see the light that shines in me
And now I can be my better self
I can free the past
'Cause now the future's bright for me
My cutie mark has set me free
What will the CMCs do from now on?
Help everypony else. On first watch the joy is that Diamond Tiara has turned her life around, but on rewatch, when you know the end of the episode, you can feel this song building excitement toward the same scenario that's moments away for the CMCs themselves! It's a celebration for both groups of characters.
Mind blown yet?
I could honestly go on about this episode, but I'll end with a couple more briefly:
You don't even know me at all
Don't understand the meaning of my fall
What my family would think if I ever
Fail at anything
Remember Apple Bloom having a nightmare about what her family would think if she got a cutie mark without an apple in it? Remember Sweetie Belle trying so desperately to make Rarity happy in Sisterhooves Social? Far from not knowing Diamond Tiara at all, the CMCs practically
are her. (Like I said, it's secretly a recap episode!)
Next up:
I'm a diamond – that means you'll never break
No matter what be the cost of the path I take
Whatever I have to do to win in the end
Diamond Tiara sings about never breaking and the CMCs sang earlier about never giving in, which are basically the same line, and they've even done it with similar perspectives. Again... parallel paths.
And lastly, to end with a bang:

It's time for a new leader
It's time to make a change
We're here to fight for what we believe
(Vote for Pip!)
It's finally time we beat her
And play a better game
By the end of this episode, we have no idea if Pip is able to do anything or if he'll be a meaningless figurehead like Mayor Mare who lets his specialized team of superstars handle everything. After all, he couldn't have been elected without the CMCs and he couldn't have fulfilled his promise without Diamond Tiara, the very same pony he kicked out of power.
So who's really going to "
make a change" by the end of the episode? Diamond Tiara and the CMCs.
Who's really going to "
play a better game" by the end of the episode? Diamond Tiara and the CMCs.
Who's really going to be a "
new leader" by the end of the episode? Diamond Tiara and the CMCs.
While this entire song is about Pip, it's meant for Diamond Tiara and the Cutie Mark Crusaders; all the talk of change and new leaders sets the emotional undertone and prepares us for all the vastly more important events at the end of the episode. The song hypes us up, but the subtle and key followup is that Pip doesn't do anything in this episode because, by design, he shouldn't. The excitement might disappear if we saw him accomplishing things, so we immediately move to Diamond Tiara for a shift of tone and focus. This leaves the hype about new leaders and change lingering subconsciously so we can circle back to it at the end when it's properly redirected to the CMCs and Diamond Tiara.
All of this combines to make up the reason why Crusaders of the Lost Mark is my new favorite slice of life episode in the series--
and my favorite action episode!
Yes, I said action episode.
And yes, I know Twilight's Kingdom Part 2 exists!
Hey,
in theory I'd prefer for MLP to be an adventure series instead of a slice of life series, which I know most fans disagree with, but
in practice the adventure episodes are rarely written with significance.
Sure, most people love the big epic laser battle or even Pinkie Pie shooting changelings with the party cannon, myself included. It's cute and fanservice-y. At the end of the day, though, those scenes aren't about anything. They're fun but isolated, with no build from what came before them and no impact on what's to come after them.
So this...

...is ultimately far more interesting
even as action than this:

For all its simplicity, this chase scene of the CMCs pursuing Diamond Tiara through Ponyville has gravitas. And for all its flash and novelty, Twilight's battle is ultimately a blurb of sound and fury signifying nothing.
Why are Twilight and Tirek battling? Because villain evil, villain smash. But who cares? Where's the heart? (I'm speaking
comparatively! I do still give Twilight's Kingdom an A- and I really like it in a vacuum, but it's nothing compared to Crusaders of the Lost Mark.)
Crusaders is action with a purpose, where even if the "action" is simple running, it's about characters running toward and running away from their destinies. It's about a clash of ideologies. It's about determination, sympathy, shades of gray, and understanding one another.
It's about characters who have real roles to play. Because the stakes aren't physical life and death, they're not forced into their actions; the stakes are the vastly more interesting
moral life and death, where the characters' choices and agency reveal them for who they are and build toward a satisfying and natural conclusion.
If you read all that babble, thanks for sticking with me!

I hope you all loved Crusaders the first time and see all its brilliance on every rewatch. The only "negative" thing I can say is that there's no way the writers can top this for me unless the endgame is the CMCs surpassing the mane six. I don't think they'll go with that plan, but that's the endgame I've wanted ever since Flight to the Finish, then even more after Twilight Time, and especially more now.