Enmity/aggro is just a damage system with a fancy name. The only reason why these systems exist in MMOs is because tanks do less damage than dps. If you wanted to create clever, engaging enmity gameplay, you might as well create clever, engaging damage-dealing gameplay. This may come as a surprise, but tanking as a concept well pre-dates enmity systems.
No, removing the stance system was one of the things that Shadowbringers got right.
How do you make tanking more interesting? There are a few ways.
1) Positioning: Force your tank to re-position the boss while evading mechanics. Cleaves are a good test of movement mechanics as well. I'm not sure why every mob ability in this game gets animation-locked, but this seems to take a lot of the positional awareness out of tanking. I don't have to pay attention to my position if I know that the boss is locked in place for the entirety of a mechanic. It's a different story if I have to dodge with a simultaneously cleaving boss that can wipe the group if turned the wrong way.
I suspect that this is something that the game inherited from 1.x, but it feels like one of the reasons why tanking in this MMO feels inferior.
2) Mitigation: It doesn't really feel like we mitigate any more. Invulns are a big part of the problem. All the relevant tank damage comes in the form of tankbusters. But these are generally spread far enough apart that they get handled with either invulns or a surplus of mitigation cooldowns.
Tank damage is either fluff or tankbusters. I think what made fights like T9 or A3S intimidating at the time was the presence of intermediate damage types, such as cleaves, which didn't have a cast bar. It's not mitigate or die, but it's the sort of thing that can burst you down if you and your healer aren't on your toes. And they have to happen frequently enough to keep the pressure on, both from a healing perspective as well as forcing you to expend precious mitigation reserves.
3) Damage: Where does damage fit into this? There are a couple of places. First, it's a concentration check. Can you do the above while managing your resources/rotation? Second, it fits into positioning. If your tank is forced to reposition the boss, a good tank is going to do it without losing any uptime (for both themselves or the team). A bad tank is going to run across the arena and let the boss run to them, costing both themselves and everyone else uptime in the process. Tank damage indirectly tests this.
That's how I would address the issue.