I don't think this is something that is solved by the presence or absence of tank stance, however.

How do you make tank positioning and movement matter? You design fights where it matters. The devs have done it before (A7S was the last memorable example). The problem is that it's easy for us to get caught up in playing as a sort of melee dps, such that we don't really notice that we're not actually doing any positioning work ourselves. The only way that we're going to see a change is if we make it clear that we don't want fights designed for just dps. We want fights designed for tanks.

How do you make mitigation matter? You design fights where it matters. Have more than 4 tank busters, such that you're used to use something different than an Invuln, Invuln, Supercooldown, Invuln rotation. Throw out punishing cleaves that force us to memorise subtle timings with resource-based cooldowns. Maybe this is just a confidence thing, but I seem to remember that raid bosses used to be much, much scarier.

It's okay to have a bit of 'optional' shared responsibility. It actually makes dps jobs more interesting to play if you can actually help your healers and tanks out. By that token, nothing is truly done by any one person, even snap enmity. Behind every well optimised add pick up is a NIN donating Shadewalkers and Smokescreens. The more prevalent these tools are, you give dps players the opportunity to feel like team players as well.

Right now, the gameplay surrounding tank stance is a bit of a distraction from these bigger, underlying problems. Only when you remove it will it become obvious how much has been stripped from tank gameplay due to underwhelming fight design. We need fights that are built around whether they're fun to tank, not just around whether they're fun to dps.