Please, don't act stupid, it's a raid of 25 people, obviously it's not split up like that. It was more like me doing around 185k with most people sitting around 150-170k and then usually some really well geared hunter, warrior, shaman or rogue sitting above 200k(yes I know gear is scaled, but you can have better itemised gear, more artifact traits and gems if they work).
Now I don't disagree with questing being shit for us, although you have to remember that it's a lot harder for everyone. Yes we are probably one of the worst for leveling due to how our class works, but it's not like other non tanks are miles ahead of us, a lot of them have to heal up between fights as well. Warlock for example plays a bit safer than shadowpriest and can survive more mobs, but it has significantly slower kill speed.