I hate to sound like Parelli here (shudders), but if his horses keep saying, “Bob, you’re doing it wrong” then maybe he should listen to them!
Some of them aren’t going to be used to full weight and standing at a block but my god it doesn’t take a Rhodes Scholar to figure out that you don’t just do those things right off the bat. Maybe he should try speaking their language for the first few rides till they get to know each other and get a line of communication going, and then introduce the new concepts? Tons of people have no problem transitioning Ottbs, save for the rare special case, so the horses are notnotNOT the problem. Are you listening Bob?