Overwatch really needs more characters who can fill the same main tank role as Reinhardt does.
I think the game has developed in a way so that it's not that bad with how he is anymore. The 5 tanks are all kind of extreme in their niches right now anyways. You have a poking tank, a diving tank, a pick tank, a fighting/peeling tank, and whatever the hell D.Va is. There are lots of different strats that those tanks fill in on. Like, Rein is the poke tank but he's trash at peeling and engaging. The only tank really super good at engaging is Winston, do we need another engage tank too? The only tank that can shield and peel in a large area is Zarya, do we need another that can do that too? The only thing about Rein is he lacks a lot of crossover abilities the other chars have.
I will say the Rein issue probably has a lot more to do with maps and modes. The fact linear maps have sections where Rein just covers a lot makes him crazy good. The fact those maps also have chokes you have to move slowly into makes him must pick (side note: when Mei started making that less appealing Rein got worse). So having another tank that can safely push a team through those spaces would be pretty nice, yeah. That's really what it boils down to, and it leaves a lot more room than just "someone who can block damage".
I think a tank that excels at creating space somewhere in a different range would be nice. The ranges that the tanks can control are pretty wildly apart and have lots of gaps. You either get Winston creating too much forward space at once or Rein slowly crawling to give you some. D.Va can do that on some maps but ehhh.
Edit: I will say that having a tank other than Rein that can reliably counterplay something like another Rein's ult would be nice too >_>