I've been moaning with alot of other Drks on this forum lately but I've come to realise that really what most of us are talking about, boring mechs and tanking no longer being fun is IMO cause by a lack of responsibility and consequences.
Aggro
Originally Dps could pull aggro off a bad tank, not all moves gave enmity and if I remember correctly most of those moves only gave enmity while in tank stance. This added consequences to the game, DPS and healers had to use moves to lower their aggro.
Tanks stance wasn't perfect, and at high-end ARR the meta was to tank without it. However removing it was a terrible plan IMO. Instead they should have made aggro gain more difficult if you weren't stance switching, made tank stance OGCD and then in each expansion they could have focused each tank classes mechanics around their stance and subsequently TP which I'll get onto next.
Resource
TP while not brilliant was better than our current system of spam all you want you have unlimited resources. Originally players had to think about their rotations, every weapon skill cost TP and speaking from the tank side that was always present in mind. It wasn't too hard for low skill players to handle (I should know I was/am one) and removing this lowered the skill ceiling not the skill floor.
Movement
Sprint used to cost TP, this used to wind me up back in ARR but I've come to realise that If you need to sprint in combat, you messed up, and therefor you get punished. The problem was that it only punished melee and tanks and not magic users.
Imo they should bring back a cost of using sprint while in combat via some form of debuff "less x done for X seconds" making it class specific for example, tanks have lowered resistance for X seconds or even making it slow you for X amount of seconds after use while in combat. It wouldn't fix wall to wall instance pulls but it would certainly go along way towards reducing it.
I realise this was our fault. We as tank players moaned about difficulty or the tediousness when really the difficulty and taking your time is what made the game fun and gave us the sense of achievement. The devs clearly have had to lean into the wall to wall instance design, if you look at all the recent expansion instances, it's two mob packs, boss room, two mob packs, boss room. Even the boss fights had to go to AOES everywhere turning boss mechanics into dance dance revolution, because we can sprint without consequence in combat anything short of a room full of AOE's wouldn't even graze us and since tanks never have to worry about loosing aggro the only mechanics they can do is don't step in stuff.
IMO to get tanking and in general combat mechanics back to a fun and health place, first we need to bring back consequences of us playing badly, be more unforgiving for our mistakes.