Pokémon week March 27-April 2

It's B- in UU. It gets outclassed by Togekiss as a special attacker, Primarina as a special-oriented wallbreaker, but does decent as a defensive mon cause it rivals Umbreon. The guy who you were playing against probably didn't have any top-tier OU (or even UU) offensive poison and steel threats.
Don't worry though, there's like 10 mons in B- tier in UU lol

i one shot marnie in pokemon sword using only a sylveon (marnie after game is beat)