Need suggestions of specific bits with a serious "whoa" factor

I really like pelhams for stuff like this, with two reins. Mullen mouth with just a little bit of a port so there’s room for the tongue.

Might also be interesting to try something like a Mikmar. While still a snaffle (sort of) it is different enough that it might get his attention without being harsh. Given what you’re saying about his “brainwashing,” something like a Mikmar might change the conversation enough to get him going down a new path mentally.

I agree with those suggesting ground work. Get that consistent whoa long lining and then teach the weight shifting, slight hand raising subtle cues. If he doesn’t long line and stop well in a snaffle, try something with a shank. Whoa isn’t optional