Eh do we need more tanks really? I feel like that the class that's already pretty well balanced and covered when it comes to utility and diversity. Just need that damn discord to go away.
We really need one more to kind of balance out the Rein/Zarya monopoly on shields I think. The tanks are well balanced and I like them, but the way comps work you're forced into running Rein or Zarya. Neither of them are broken and the other tanks don't need better shields or they'll just break themselves. So following that line of logic introducing a new tank that can really focus on a different way of shielding/mitigation would help fill out that pool.
Every class needs fleshing out though. DPS has it the worst right now in some ways because defense heroes all mostly fall into the DPS slot. There's room for niches to exist in the DPS slot, but for some reason all the niche DPS characters at launch are based around static defense or area control. I don't mind there being lower pickrate or map/comp specific heroes in their own niches. What I'm sick of is that all of these heroes fill the same niche. Would love to have a utility based character in the DPS slot I could run on offense or more fight based comps.
Like the DPS slot has the most heroes, but it also has insane amounts of overlap that is really starting to bug me.