[Senkusha]

We know from the movies that Percia was very rushed with Fate's magical training.  This is why Fate concentrated on speed and agility and a very select number of magical spells and attacks.  She didn't really have the luxury of time to dedicate toward learning new techniques and other realms of magical aptitude.

But just consider for a moment just how powerful Fate could have become, had she been afforded the quality amount of time to dedicate toward a true study of the magical arts.  Granted, Fate is a quick thinker as well as being lightning fast physically.  That's part of what defines her as an overall character, almost like as if she were a trope.  She's the fast girl.  But she has a number of other qualities that are often overlooked or simply forgotten about.

She's smart.  Like wicked smart.  It seems the only subject in school she has trouble with is Language (I believe it's Japanese, referred to in one of the manga.  Fate is also highly compassionate.  This is identified in the movie Reflection (I believe).  Of course, we can't forget the sheer amount of determination and willpower Fate possesses.  Again, this is referenced in Detonation or Reflection, but also in the seemingly daily pursuits in the TV series against whichever foes she's battling.  Fate just keeps standing back up, ready for more.

If she were able to fully concentrate on other aspects of magic, I believe that Fate Testarossa would be literally an unstoppable mage in the Nanoha Universe.