most of the confirmed Fairy types have very low BST
None of the BSTs were confirmed for any of the Pokemon yet o.o
Wigglytuff, Azumarill, and Gardevoir all have near 500 BST or lower. Sylveon will have 525 BST like the other Eeveelutions. They won't be able to do much even with type advantage to say... Salamence. Or else you would see more ice types as dragon killers instead of people packing ice moves.
Remember remember... the 30th of November. The day that heroes could not save the world. ~In remembrance of City of Heroes.