On brokenness: I think that it's not so much that Twilight's
talent is Magic, so much as her
passion is Magic. Even before she had her freak-out and got her mark, she was fascinated and enraptured by magic in all its forms. And after becoming Celestia's student, she poured all of her time into study and research.
Yeah, she started out with some Gohan-esque untapped potential, but she's only reached her current level by making the study of magic her entire life
for pretty much her entire life. She might have started out with a leg up over some other Unicorns, but it was only because she spent years and years of
sleepless nights
working on it that she got where she is.
Other unicorns, I do believe, aren't interested in magic as a whole, so much as they are interested in learning and perfecting the spells that help them in whatever their own passion is.
I mean, just look at Rarity. Fine-tuned telekinesis and item animation, on many different items at once, to make dresses with precision and style. Heck, in Sweet and Elite, she was seen making the foundation for the dress with just a flash of magic.
I believe it was either Bruce Lee or Jackie Chan who said that they feared not a man who has practiced 1000 kicks 1 time each, but the man who has practiced 1 kick 1000 times. Twilight is an example of someone who has practiced 1000 kicks 1000 times,
at the expense of everything else.
I have a message from another time...