Okay I can see what your getting at, but Twilight can concentrate her time pause magic to who it can effect. If I can remember correctly Spike wasn't effected was he?
I'm going to assume for now she can basically control who she's effecting with her magic. Not to mention she has other non lethal spells she could've used to trap her long enough for the others to think.
I dunno I kind of thought something could've been done.
And Fluttershy can be OP at times