Your M+ Group lives and dies by your tank. Frankly trying to get to 20+ on all dungeons just burned me out and I've been sitting on 18s with barely a will to log on. The tank needs to set the pace of the run, establish the route....fix the route when someone screws it up, keep himself alive all while optimizing his own damage to make the run go quicker and not lose aggro, while establishing positioning. You're also a huge source of crowd control.
I played mostly my healer in BFA, and sure while it's a thankless role, all I really had to do was sit back and not die, naturally when you get to higher keys players get better at avoiding damage. Hell there have been times I'd die as a healer on Tyranical bosses at 50% and we(they) still manage to pull it off.
Healer dies you pinch your butt cheeks and avoid damage till he comes back. DPS dies you roll your eyes and keep it moving knowing some time needs to be made up. Tank dies shit automatically hits the fan.
My memory could be distorted but I felt like Legion wasn't like this, granted this is before Raiderio so people were less hardcore, once you got your Keystone Master people didn't care much about timing keys. But in Legion the threat multiplier was insane so losing aggro was not a thing. You had to be extremely careless to die as a tank, I don't recall as many tank buster abilities and most trash you could just AoE stun down and their abilitis weren't very interesting. Aside from a select few mobs per dungeon, none were very dangerous.
Overall even though tanking has always been a critical role, I felt that a bad tank could be carried almost as easily as bad DPS in Legion if you could just stun and killing everything before the tank got themselves killed.
With that said Legion tanking kind of just felt like you were just DPS melee that stood in front of mobs opposed to behind them. Tanking was far more engaging in BFA and now Shadowlands. I'll dare even say I kind of enoyed the kite meta, the emphasis on keeping your self alive while maintaining control of mobs. Utilizing your CC to prevent deadly abilities and many mobs can't simply be stunned any more, so you have to play around such enemies.
I think my biggest beef is simply needing to be the guy that knows the route, and because M+ is timed it's not like you can take a breathe and ask your teammates for directions. Some of my more prefered dungeons to run are the ones where the route is damn near impossible to screw up like Theater of Pain. In Legion the routes were freaking obvious, if you could walk around a mob....you did, and it's not like Prideful was a thing.
I'll admit I always get anxiety when I run Plaguefall, it's supposed to be one of the easier Dungeons, but I know my route is outdated, so after all the work I put in to originally learn a route initially starting at key 10+ to key 18+ I need to backtrack to about a 15+ to memorize a new route.
Almost feel like just swapping to my healer sitting back and enjoying the ride.