I can't make someone change their way of thinking. But that's also not my job. I'm just here to offer an opinion.

I think that the end goal should be to create distinct ways of performing core tank functions. Let's take mitigation as an example. How can you reduce the rate of incoming damage?

1) % Damage Reduction
2) Max HP buffs paired with self-healing
3) Flat Damage Shields
4) Stagger
5) Rewind damage received over past X seconds
6) Debuffs (Slow, STR/INT down)
7) Directional Shields (i.e. Passage of Arms)

What movement abilities can a tank have?
1) Gap closer to target/ally
2) Set up teleporter between two points on map
3) Increase movement speed
4) Gap close to a specific point
5) Pull mobs to you

The starting point is wrong. There's no point giving everyone % damage reduction abilities (i.e. Sheltron/Rampart/Sentinel/Hallowed) and then trying to balance them. That's a math question, and there is going to be a best option that people migrate to. You have to start with alternate approaches, and find a way to make them feel equivalent. Some people are going to want to buff their max HP, followed by a burst of lifesteal to survive a big hit. Others are going to like seeing incoming damage just get negated while they launch a series of counterattacks. Or what if, as the boss hit you, they just started doing progressively less damage? The goal should be to create unique experiences, and then find balance between them, despite there being no way to mathematically correlate those effects.

I'll say this. The community response of "Where's my X ability" is the biggest culprit here. You never needed your copy of Reprisal. You didn't need your copy of Plunge. You don't need your carbon copy of TBN. You need to find your own way of achieving the same goals. And a dev team that only knows how to cater to these demands as a means of putting out fires just perpetuates the cycle.

I think that's the one thing that Blizzard is pretty smart about. That and the fact that there's at least some level of interaction between the devs and the playerbase.