It's a bit difficult to follow the reasoning of this discussion because of phrases like "niche mitigation skills". Which specific cooldowns are you comparing, and what warrants comparing these abilities in isolation instead of looking at the kit as a whole?

To the best of my knowledge, every tankbuster set in the game can be mitigated between you and your cotank, regardless of the jobs that you pick. The difference is that in certain fights, a tank job will occasionally have access to additional cooldowns that may make healing easier, or that allow you to drop stance more comfortably to push your dps while tanking.

Your core mitigation set is still Rampart/Sentinel/Hallowed. Every job has equivalents to these (some are better than others in certain situations). I suspect that the mitigation moves introduced with HW were part of a broader move to balance out IB, which is probably the most versatile cooldown in the game. It's still quite powerful in HW, but you're now rewarded for not being overly dependent on it. This was a sensible course of action: if you have access to a short recast cooldown that can be used for both physical and magical attacks, you're just going to mitigate everything with it, which defeats the purpose of designing a cooldown rotation.