I have to support the OP, the difficulty gets outrageous. You would think the rewards would improve.
You say that the difficulty goes up as your ELO rating goes up, but does this also mean that the difficulty goes back down when your ELO rating goes down? I could see games getting so difficult players would be inclined to throw games to get it back down to a fun level again.

You should really consider either making the enemies less difficult, and if not please improve the reward and add an option to CHOOSE your multi-player difficulty.

I'm really having no fun lately, no fun at all. And if this is what you want, then that's sad. I am getting to the point where I logg in and stare and sigh because I don't feel like the headache. The fact that this was a multi-player Co-OP was really good, I got tired of PvP all the time on Overwatch and wanted a more raid like feel. The Antag system was bad enough that I had to put up with, and worse, participate in in order to get to use weapons you "win", but the difficulty raising makes it so that I can't look forward too relaxing and having fun doing PvE.

Please consider looking into this.