I agree that Vision seems lopsidedly good for the protection tanks, as it benefits their comparatively shorter CD DPS cooldowns rather than the longer CD defensive cooldowns that they both possess.
I understand the desire to have some essences that are more beneficial for some specs than others, but my suspicion is that this will end up the only essence considered for Paladins and Warriors in mythic plus. Everyone has grown pretty accustomed to running dungeons with existing defensive capabilities, so the value of taking additional defensive options is pretty low, while boosting damage remains a priority.
Not only is sporadic uptime and cooldown reduction of Wings and Avatar not problematic in terms of value, but both specs have strong talent and trait synergy with these abilities that will push them further ahead in damage dealing, where neither tank is particularly hurting at the moment. This seems like the sort of decision that could make one or both tanks the clear winner(s) for the duration of the expansion.
The essence could instead apply to Shield Wall and Guardian of Ancient Kings, which would be the closest analogs to what the rest of the tanks get, and would leave all tanks more or less with the same array of effects from essences, which I think would be fair. Performance in both DPS and survivability is pretty disparate on live, so if anything, the essence system should bring them closer, because balance in an MMO matters.
Alternately, we could all just swap to paladin or warr.