PvP Teambuilding and help?

I've gotten to A rank, up until this point I was doing pretty well. Even got a 13 kill game yesterday! But once I hit A rank, Jesus the amount of teams that ONLY have mythicals. Hoopa one shots practically every one of my pokemon, literally every game I try to swap out something only for it to get instantly deleted once I bring it in.

My team was a Metagross, Swampert and Golisopod for the 13 and was my general use team for season 4. But I just keep getting instantly deleted, and none of my moves were doing nearly as much damage as anyone else's(like I swear everyone else's Swampert hits WAY harder than mine and I fail to understand why)

This is definitely an anger induced post, cause I've just been having terrible matches all day and I'd like to know what I should be looking out for, what pokemon I could try using to see better results and etc.

If possible I'd like to keep the Golisopod, he's a tank usually, but it seems like even neutral hits from any of the mythicals just delete it instantly.