It's past time, Yoshi-P...

[Zfz]

the only way to improve on tank enmity and mitigation rather than just focus on “tank DPS” would be to scale content and make it “harder”/more difficult

I disagree. As a very simplistic example, we can make tanking enmity equivalent to tanking dps, i.e. by removing the damage penalty and making different stances suitable for tanking different things, then removing enmity bonuses and changing "enmity vs dps rotations" to "single target vs aoe rotations". Give tanks a moderate innate enmity bonus if you want to make life easier for leveling and entry level content.

You think there's only one way because you're thinking of minor adjustments, minor tunings based on the existing framework. I'm talking about a change to the core design itself.

Or more elaborate design changes can be made such that tank damage output becomes a derivative of enmity established on targets, instead of having enmity being a derivative of damage done on targets.

Mitigation can be elevated into mostly a strategic decision, i.e. gearing choices, and keeping the scripted cooldown schedules for the sake of assisting with encounter design. Secondary stats could work differently for tanks, with Tenacity giving passive mitigation, SkS reducing cooldown time, Crit giving a chance of randomized mitigation effect (e.g. one out of 3 different mitigation effects like "10% less damage for 5 seconds"/"shield worth 10% of healing received within 5 seconds"/"parry and block mitigates extra 25% damage for 5 seconds").

As such, I argue that there are possible designs to do what I said.

However, all this may be moot because devs seem happy about where the tanking design is at the moment. So this discussion is mostly academic.