You do know that you have five other mons to take care of the special walls the CM set on Sylveon can't beat? There is team preview. The smart play would be to figure out what the opponent is running, see if there are any special walls (like Blissey) that need to be taken care of, and then start CMing AFTER the special walls are gone.This kind of sets I hate, you are WALLED utterly by special pokemons, namely Florges, Sylveon, Mega Blastiose, Blissey (omg Shadow ball doesn't do even 1%) going for Wish you'd easily be 2HKO-ed by a lot of things if you don't Protect, going for Sub you don't have a healing move and you fail as a wall. Sorry but this set, I don't see t balanced.
There is merit in a CM Sylveon set. You have to run it smartly, like any other Pokemon moveset.