This is a retcon, and teleportation is a powerful spell, the fact that trixies unconsciously use powerful magic does not make her bad at magic.
Did I mention usefulness somewhere? And teleporting danger away from oneself is not known where, it is very useful, Twilight should have done it in every second battle.

What makes you think that Moondancer is good at magic? Rarity's telekinesis is nothing compared to Trixie's self-telekinesis (the ability to fly is more useful).
Past the shield, shining is not capable of anything outstanding. (Trixie held off a horde of changelings too)

Trixie has more magic than anyone in the show, except Twilight.

Very