That's sort of what I'm wondering, it just sounds like an entirely different vocal that I haven't heard come from Mike before. I'd like to think they're doing it together, because like you pointed out there's definitely a higher harmony, and a lower harmony. My only other "evidence" that Chester is on the chorus is the placing in the track list, could be nothing, but all the Chester tracks are grouped together and then the Mike tracks are grouped.
If it is all Mike, then damn, he can sound like Chester in a way I've never knew. I figured Mike could carry the band alone, but this song shows he could do some of the old Chester stuff as well.
One other thing, the way the word "controlling" sounds, that may not even be the word, sounds like how Chester says it in another song but I can't think of it off the top of my head.