You don’t need tanks to help charge healers, though of course they’re safer options if you must do it. In general you don’t just want to soak damage because it feeds the other team’s ult. The best tanking in overwatch terms is taking damage off the table.
Roadhog for example is, IMO, a poor tank right now because he’s that MOBA style tank that is meant to just eat damage, but he is easy to avoid in a general sense (unless you’re hooked you just ignore him tbh, and in many ways you just ignore him if you are hooked), and just charges up the enemy.
But that style of tank is actually detrimental to the team in many ways, they should dump him in to the offense category and do whatever small tweaks they’d need to do in order to make that work.
DVa has just been moved closer to Roadhog, that’s not a positive thing. Until they make it so that tanks like Roadhog and now, to a lesser extent, Dva don’t feed Ults as fast as other characters then the “I’m going to be fat and get in your face” tank is a failed concept.