I think Bylsma's problem was that he was just kind of a doofus and wanted, sooooo f***ing badly, to be one of the dudes again.
Sullivan's been propped up on this pedestal and only ever given obscene positive reinforcement since the back to backs, so his ego just completely ratf***s any bit of sense or strategy might be in that Masshole noggin of his. He'll stubbornly torpedo things seemingly out of spite just to try and make his way work, because he'd rather be vindicated and proven correct than change and admit his approach to any given situation/decision was wrong. Deeply unlikable presence on the team--butchers the entertainment value with his style to boot.