How good is Snorlax competitively? My first online with it was surprising.

A passerby challenged me even though I didn't have an EV/IV trained team at the time so I just played with the Pokemon I won the game with. The guy was playing with Yveltal, Xerneas, two Mewtwos, Greninja, and something else I forgot but I'm sure it was another legendary. I thought I was going to lose this one but when I sent out my Snorlax after my first Poke was swept it went off.

Snorlax had Rest, Snore, Body Slam, Crunch. It forced the guy switch like 4 times because he couldn't kill him. It left two of his Pokes paralyzed and actually one shot his Greninja. He eventually disconnected.

Was my opponent just bad or is Snorlax a beast?