I do not buy this story. JB Is incredibly outspoken, and has no problem airing his grievances in public. Fights with shoe companies? He will be loud about it. Olympic snub? Of course we will hear about it. League awards he is passed over for? Yeah, he will complain about that too. Refs? Sure, despite multiple fines. But he will instead send Tracy McGrady to agitate about the Celtics? No, that is just not his MO.
I am sure he has some grievances. He probably has some about how he is used on the court, he might have some about someone in the locker room, he probably has some about how the Celtics promote him, and he very likely has some about Boston in general. For better or worse (and often for the better in my opinion) grievances are what fuels him. Accordingly, I am sure Brad knows about all of them. Will Jaylen be traded? Maybe, but it will not be because he forced himself out or just made life unpleasant.