I like the concept! But I don't like how tired my arm gets after just half a session haha.
My suggestions for fixing that part might go against the mayhem philosophy you had, but to spare the players hands it would be nice if you didn't have to spam while keeping it hectic.
What if instead of spamming the buttons, they functioned as toggles, that you have to time optimally for maximum production. You already have indicators for the combiners as they fill up, so what if you had more of them that you toggled between, that fill at different rates, so you got to keep track of the more combiners you add, swapping between them as they fill up. That would also make the upgrades for faster autogeneration something that does something, since now it barely has any impact.
Great music, and nice Slap-in-your-face UI!