You don’t have to. You can do rated pvp or push raiding. Mythic+ is just another route. Even then, 15’s are pretty easy to farm for easy vault loot. The competitive side doesn’t really start until you hit the 18-20+ brackets.
I know plenty of people that hate keystones and they gear out via rated bgs and running 3’s.
And if you don’t want to heal anymore, don’t. Do what you enjoy. I used to be a raid lead and main tank for at minimum 5 raids a week. It burns you out over time. I strictly dps unless I am doing leveling content or bum rushing normal dungeons for friends.
It’s not. Just don’t assume everyone is talking down to you.
Honestly, the game has changed to be more so geared towards progression raiding. If you noticed this last tier was pretty insane on the difficulty level. Heroic anduin was giving A LOT of guilds trouble. Jailer wasn’t a cake walk either, but it says a lot that anduin was a pretty big wall for a good population.