But she's not. She's a huge scaredy-cat, who has to relearn overcoming her fears, time and again, because it's so ingrained into her persona - and probably because, given her attempts to bolden up, she'll overshoot and wind up either staring people shitless ("Dragonshy", "The Stare Master"), snapping and becoming an affection-seeking psychopath ("The Best Night Ever"), or turning into "New Fluttershy" ("Putting Your Hoof Down"). I still love her character in spite of that, but I she's most assuredly not perfection incarnate.
Well, I'm a Fluttershy fan, but unlike you, I don't like her
in spite of her flaws, but
because of them, as much as I do for her qualities.
(just how boring would a flawless character be anyway?)
I think your wording is a bit unfair though, you make it sound like her character development is ignored and repeated in following episodes, which I haven't seen happening.
It's not like in "Dragonshy" she learned not to be scared of anything (how could you turn from cowardly to brave overnight?), but to overcome her fears for the sake of her friends, in emergency situations; in fact, at the end of the episode she's still scared by a leaf falling on her back.
But she showed that she learnt her lesson in "Stare Master", where she forced herself to enter the Everfree Forest alone and face the Cockatrice for the sake of the CMC, despite her comically displayed fears, and without any of her friends pushing her this time; she didn't re-learn the lesson either, what she learnt in that episode was something about not biting off more than she could chew.
In "Hurricane Fluttershy" she clears this up herself to Rainbow Dash, saying she could fly just fine in case of emergency, but not for a performance: that's an entirely different kind of fear to overcome, and she does it for the first time at the end of the episode.
I also appreciate how she learns to be more assertive in everyday situations during "Putting you Hoof Down", and is later shown strictly refusing to comply in the intro of "Dragon Quest", displaying a completely different attitude from the one she showed during "Dragonshy" in similar circumnstances.
So yea, while Fluttershy is as flawed as every other "mane-6" Pony, and will (thanksfully) always be for the sake of comedy and entertainment, she's also shown no small amount of improvements and development over time.