If you load in split screen to exchange gear with a mule etc then return to single player (and even offline single player) the game scaling seems to be 4 player.
For instance normal mode mayhem 3 slaughter shaft round 1 starts with 5 anointeds. So 4 to 5 of the teleporting ones or a mix of them and marauders all attacking simultaneously.
I’ve watched tvhm m3 solo play and at most I see 3-4 enemies with the majority non anointed.
Tested with wave one and two.