You are wrong. If what you claim were actually implemented, it would create an attack vector where the sender creates a payjoin transaction at a high fee rate and burns the receiver's input.
Dude, I'm not going to argue with you suffice it to say, that's not how it works. This is not an inclient function this is a coordinated out-of-band operation. You don't just get to "set your fees." Go read this: https://payjoin.org/docs/category/how-it-works/