There are 3 cloth classes - Mage, Warlock, Priest
There are 4 leather classes - Druid, Rogue, Monk, Demon Hunter
There are 2 mail classes - Hunter and Shaman
There are 3 plate classes - Warrior, Paladin, Death Knight
I mean yes, there's going to be more competition for leather gear initially, but realistically, few people play Rogue or Monk now on live, and a lot of them will be the ones jumping on DH. I mean look at me, I'm going from a Druid main for 4 xpacs to possibly playing DH. That will be the same gear type as before. I think after the initial hype dies down, and especially if the initial feelings are negative since leveling a DH from 100-110 is going to be a shitty process, it should balance out OK. It all depends on lasting popularity. The popularity of Hunter alone makes mail gear harder to get.
I don't really feel like I "should" play any class for any particular reason. I think Legion is in a better place now in terms of, I can pick the spec I want to play or feel I am best suited to, and roll with it.