I don't know, I don't think Androxus (the reaper looking fellow) is terribly OP. He's pretty fragile, has a relatively short effective range and his dash doesn't take him all that far. I've shot plenty of Androxuses and Drogozes out of the air with Cassie. I do think he rewards good play though, you really do have to flank or you will die terribly every time you run into an enemy.
I don't really feel like there are any characters that are terribly OP at the moment. I don't think everything is perfectly balanced either, but it's still in beta and changing fairly regularly. There are definitely characters that feel a bit weaker than their counterparts though.
My biggest issue with the game right now is that hitboxes really do seem overly generous. That and I think the replay system isn't perfect so it frequently looks like people are shooting people they don't have LOS on in the death recaps.
It's funny when I first started playing I thought most people who played the game were terrible at it, but then I found out later for like the first five levels you are only playing against bots. The game, as far as I know, never tells you this and the bots are named in such a way that it isn't immediately apparent that they are bots.