Is he an insufferable asshole, borderline incompetent in the HR department, and generally a dick about how he goes about his business?

This isn’t the cut and dry yes you think. Starfleet is a military organization. Jellico was perfectly reasonable, possibly even downright pleasant, as the captain of the ship. He is the commanding officer. Junior officers do not need to know his every thought and rationale for every order. The commander sets the tone and expectations for his crew. Jellico wasn’t Picard. Didn’t make him an asshole, just not the same command philosophy.