Perhaps you could outline what you would consider development, since the show has apparently never done any of it.
edit:Here are the major ones I'd highlight:
Twilight:
First season: An awkward nerd who realizes she wants to become more social but is terrified of failure. She sees her friends as a test she will pass or fail. Episodes like "Boast Busters" feature this. She is a talented unicorn (compared to other ponies). "Cutie Mark Chronicles" also gives us her life goal: To be like Celestia.
Second season: She realizes her bond with her friends is more than just pretending to be perfect. "Return of Harmony" and "Lesson Zero" especially hammer on it. Her magic is more refined, as in "It's About Time."
Third season: Twilight is groomed for leadership. We see the princesses nudging her in that direction in "Crystal Empire" and "Games Ponies Play." "Magical Mystery Cure" is the conclusion of her three-season story arc. She becomes like Celestia -- powerful with magic, strong relationships, a confident leader, and now a princess (although that last one is not really important compared to the others).
Rainbow Dash:
In the beginning, she is a cocky, loudmouthed showoff. She wants to join the Wonderbolts, but even with her status as savior of the world, she's not a shoo-in. By "Wonderbolts Academy," we see that she takes her position as a leader and a role model more seriously, and in the Equestria Games story arc, she is actively mentoring younger ponies, particularly Scootaloo.
Fluttershy:
Admittedly, her growth has been more single-note, but she has gone from, "That pony's scared of her own shadow!" to having a test of wills with Discord and
winning, and gradually placing herself in more public roles, like putting on the fundraiser for the animals.
Rarity hasn't had a character growth arc so much as success catching up to her, but she has now achieved her goal of being recognized for her talents among the upper class of Canterlot.
