I have to say I rather like Twilight's original cutie mark/character concept.

That is to say, she was basically the same character personality-wise, and she was seemingly the main POV character/protagonist for the show, but she didn't have that whole messanic aspect that show Twilight ended up with. Never mind becoming a princess/alicorn, she wasn't supposed to even be anything particularly game-changing in the long run in any kind of "friendship is magic" sense.
Her bio mentions that Celestia sees huge raw power in her and she might be the most magical unicorn of all someday, but then again Rainbow Dash's hints even harder at some great high destiny, such that you get the feeling the show never intended either of them to get there. Twilight's unicorn magic seems to be about casting light in dark places; whether literal flashlight-style or metaphorical, that's it. No teleportation, no shields, no rainbow lasers, nothing. She seems to be conceived of as pretty ordinary, and meant to stay that way.
And no "center of the universe, with five friends backing her up" cutie mark either. Just a symbol of nighttime, because she pulls all-nighters studying.
Which makes sense considering what the show looked like at this stage; this is pre-Elements, pre-Nightmare Moon. there's no sense that it's got any concept of a long-term serialized story to it. It sounds like just a bunch of slice-of-life stories: a premise and a universe, a place where you can create endless episodes of what sounds like nothing so much as a horsier, more bucolic MLP Tales.
I feel like the serialization aspect and the addition of the Elements mythos is a big part of what drew in the adult audience. If the show had stayed episodic like this, it would have surely been well regarded as another success in the post-Tartakovsky-McCracken cartoon world, and it would have received plenty of plaudits for being smart and funny and well characterized and beautiful. But I feel as though a major factor in what attracted bronies to it was the idea that on top of all that, there's
also this whole "prestige TV drama" aspect to it, the feeling that this could be like Lost or Breaking Bad, only with cute cartoon ponies. Everyone tuned in to see where it was
going as much as to see where it was now. (At least I sure did.)
Twilight as a messianic world-saving character who undergoes metamorphosis and catalyzes fundamental changes in the universe of the show is a pretty big revolutionary idea—and I'm not even talking about actually getting wings, I'm talking about having the show revolve around her changing and growing
over time and evolving toward a clear and inevitable goal. Most of S1 was purely episodic, but the stage had been set by the Elements of Harmony two-parter and each successive episode showed Twilight gradually getting more and more comfortable both with magic and with dealing with her friends, so you really got the sense that there was something great in store in the future, not just what we were looking at right now. The fact that the show was retooled to allow the characters to grow
at all seems to have been the key ingredient in what made the show such a crossover hit. I mean surely all the other pieces (art, character, comedy) would have contributed, as indeed they have, but I think this is the one that tipped the balance and allowed it to achieve critical mass and meme significance. Look at how much of the early fanwork centered on the Celestia/Luna story and its fantastical implications; it just fascinated people that such a thing could even exist.
Does this make it a better show
for kids though? I'm surely no expert on that, so I'd only be guessing. I kinda think it would. Kids like long stories just as well as they like short ones; they have better attention spans than they're often given credit for. I've been listening to the Tolkien Professor podcast lately and he's been talking about a Hobbit camp he's been running for kids in like the 10-14-year-old age group and he's just floored at the quality and depth of the questions and insights the kids have, even on the long-form material like LotR that takes them weeks or months to read. So probably the intended audience can appreciate the published Twilight even more than they would have enjoyed the episodic pitch-bible Twilight.
But that doesn't necessarily mean I wouldn't have liked to see what the show might have been like without all the mythos and without Twilight as the game-changer. Maybe it would have developed an even richer and funnier and more heartfelt texture than we ended up with, since it didn't have to periodically feature Big Bosses and rainbow explosions and (often clumsily handled) portents of great things to come; one of the biggest and most persistent complaints about the show from people on this very board has been that the show just doesn't seem to be cut out for handling subjects like immortality, ancient evil, the roles of Celestia and Luna, the actual nature of the world, and all the other things that we inevitably have to start asking if the show makes noises about playing in the big fantasy leagues. You flirt with a mechanistic magical universe and either you go Harry Potter/Wheel of Time and exhaustively define how everything works, or you go Star Wars/Tolkien and you play coy about it, but either way you have to show all the realistic consequences of the depth of the world you've stepped into up to the knee. You can't keep acting like villains on the order of Discord will make sense forever if you've one-upped them with one too many Tireks.
But then again maybe without the mythos aspect to it the show would simply have been missing something, the one thing that would have put it over the top and earned it our lasting attention, despite its fundamental flaws. Maybe it would have ended up as just another Sym-Bionic Titan or Mission Hill or Samurai Jack without the finale series: well loved in its time, but short-lived and as quickly forgotten by everyone except animation nerds.
Lol @ the glaring-in-retrospect "uhh can't we add some pink to her design" from Hasbro though