Both of mine are at r2, and outside of Arena, I almost never use Diablo for any content, so I’d say go with Overseer, who gets off the bench more often.
Diablo, if you run MD. He has some great utility, and if you find you don't need that particular skill you can just not activate it and shorten his ramp up.
Comments
Diablo is fun but I feel his value has dropped a bit with increase in the number of better mystics