Human accounts and generally the main content creators on top of it. The ones who create posts, the ones who drive discussion and commentary.
The bulk of their ad revenue probably comes from lurkers and consumers, but their platform is built entirely on the aggregation of a small subset of the power users. You need both. He doesn't seem to really understand that. Sure you can replace mods, maybe they're better, maybe they're worse, but you can't replace content creators and force conversation.
He's definitely sweating bullets by the way he's throwing everything at the wall to see what sticks.