I keep getting told to switch to fire or get kicked from group because I play frost mage 
It has happened several times already in the last week. I like frost I think frost is fun, but groups do not like frost right now.
Frost mages are good in mythics, they just fall behind a bit in raids on those type of long single-target fights. You probably just ran into some wannabes who saw the raid dps standings and think that means it’s the same for mythics.
Fire is top dog in Mythic+, but you shouldn’t be getting kicked for being Frost in M+. Did 50ish runs of M+ this past week, and I saw many other Frost Mages in addition to myself, none of us were ever asked to switch.
If you want “fun”, run normal dungeons. Mythics are for players who want to challenge their skill levels.