There are tons of problems, but none are as big as role balancing IMO.
I have seen others above cite “power creep”. I don’t think power creep is all that big an issue if everything is crept upward at the same time.
However, I believe Tank is once again going to become a bigger problem later on.
They are so tanky, that there is less room in their power budget to power creep them as much and/or as quickly as everything else.
At some point, tanks are going to feel awful or DPS are going to feel awful, depending on tank power down the line, regardless of their own power creep.
Tank survivability needs to be brought down to a reasonable level. They need to have counterplay based on player skill, rather than simply using stat-check balancing or mechanics.