Tanking is about helping your team to perform more effectively. Most people can tell you when you're tanking well, but often can't tell why.
The reason why a lot of beginner to intermediate tanks fixate on mitigation and enmity is because errors in either of these are obvious and everyone calls you out on them. You can fairly easily develop a reputation for being a 'good tank' in your local community of friends by just having the gear to not fall into these pitfalls regularly. That doesn't mean that what you're doing is actually good tanking, and you only realize the weaknesses in your play when you see another tank doing a better job in the same fight. The problem is, you can spend years doing a fight and still not realize that there are better ways of doing it.
A lot of what we do is based around positioning. A7S is probably one of the best fights this game has ever designed from a tanking perspective. Position the boss so that melee can continue uptime during bombs. Position yourself such that when the boss jumps to you during jails, your team can swap off of the lock and on to the boss without having to reposition. Slow backstep during cat phase so that your dps don't lose uptime, while simultaneously maintaining distance so that the heart has maximal travel time. Target lock and swivel around the boss and stun the heart just as it comes towards the boss for bonus points. When you watch a good tank doing that fight optimally, it's amazing how many thoughtful little things you can do to make your entire team play more optimally. I wish Miyuki still had his old videos from A7S up. They put most tanks to shame.
The reason why Stormblood and Shadowbringers fights are weak when it comes to tank design is because the boss controls most of their movement independently of what we do. This is likely an anti-frustration measure for your dps, but it also completely removes the need for tanks. That's fine if you want to turn tanks into a subtype of melee dps with frontal positionals who do defensive quicktime events every so often. But we'd need to see a substantial boost to our dps to support this kind of gameplay.
I think the devs need to recognize that making a role overly accessible inevitably comes at the expense of impact. Anyone can play it, but nobody wants to.