Kuzman would instantly be the most valuable character in the game.
Not particularily, at higher difficulties having a team that knows how to spread out aggro is more important than having a single player drawing ALL the aggro. I see Kuzmann go down plenty when they get overwhelmed and that big boy isn't running anywhere. People forget, as enemy health increases he is a lot less effective.
As for a Horde-esque mode it's already built into every mission structure except in reverse as far as rewards per time go. More modes period are good for the game but I think we might only realistically get one more around or after the last campaign drops. I do hope they consider your idea or something similar and not worry so much about fracturing the community between modes. They could also introduce new modes or variations on missions as events as it's something the game could definitely can and should borrow.