Doesn't Wayne Bennett in fact have a history of doing exactly this?You can't seriously think trying to undermine him and pressure him through the media would be acceptable. That would be a dirty, underhanded thing to do and very distasteful. I firmly believe you deal with things in an up front manner so everyone know's where they stand. No need to conduct yourself any other way.
If there have been conversations behind closed doors about Boyd behind closed doors and he is digging his heels in as you say, then the coach drops him. If he doesn't, that's 100% on Seibs. I doubt Boyd has the power to keep himself in the team if the coach thinks otherwise.
As I have said before, I know Seibs sets markers for every player and that determines where they sit on his depth chart. If Boyd wasn't meeting them, he would get dropped. That's probably why he doesn't think he is as out of form as he is, because the coach and others I'd guess are telling him otherwise.