It’s not that he’s less nice, because in Dean’s mind he thinks he’s being just as good a guy as always. He just takes all decisions into his own hands, tends to do whatever he thinks is best, and won’t really take no for an answer. It’s like high-level big brothering, because here, the younger one won’t argue back with the giant that captured me.
And therein lies one of the big differences between Sam and Jacob. While they might both seem like shy little mini-Sasquatches, Sam is far more likely than Jacob to tell someone off. Jacob doesn’t like confrontation and he will avoid it even if it means silently dealing with Dean’s well-intentioned but stifling protectiveness.