I think I've read that Damon takes less direction from producers now and mostly just produces the albums himself, which is kind of a shame. Gorillaz benefited a lot from Dan the Automator and especially Danger Mouse. Plastic Beach was great, especially for it's theming, but Humanz felt unfocused and bloated. A different producer might have helped that.
Also, I don't see Murdoc as a cutter. He has much more subtle ways of self-harm. Like self-sabotage and substance abuse.