Prowse has been lied to and screwed over by Lucas from day one, so I’m not surprised he was “acting as jerk”. I certainly trust him more than Lucas when it comes to the history of these movies, considering Lucas’ entire version of events has been contradicted by other figures in one way or another over the years. It seems more likely to me that Prowse was banned from LFL events for not sticking to the ‘official story’.
Nobody is claiming Lucas to be a saint.
But Prowse was in hot water the moment he leaked the ESB twist well before the film ever came out. He was also never hired to voice or physically (as in, out of the suit) play Darth Vader, Lucas just said he might be able to; not to mention he was barely in ROTJ and fired before the mask scene was even filmed. This stuff happens all the time, and that’s hardly being "lied to."
Prowse is not some poor innocent victim nasty old Lucasfilm bullied for fun.