Anthill, all you have to do is read posts on this forum to discover that many pilots are not very smart.
I don't quite agree with your view that the opinion of how good a bloke the S/O is or that the Captain is a 'known personality' is not relevant. I do agree with your two points in the second paragraph. I believe that these issues of personality and fact/competency are related. I am sure most pilots have seen personality types that can deal with differing views and manage the flight deck environment such that all crew feel confident they can speak up if they are not happy. Such personality types tend to 'bring out the best' in people and every one feels they are working together as a team. On the contrary, some personality types turn the flight deck in to an arena to showcase their own ego, and everything turns in to a pissing contest.
Managing and dealing with conflict in the flight deck is a management skill that is required from a Captain. Dealing with a difference of opinion over a technical issue should not be a big deal (regardless of whether the other crew member is right or wrong), especially if the aircraft is on the ground.
If the 'known personality' is a F/O or S/O and the Captain has good management skills, I believe the command position of the Captain helps to settle or resolve any flight deck conflict. If the 'known personality' is the Captain, it can be extremely difficult for the remaining crew to deal with the situation. This is why there is some relevance to the situation of the personality types of the people concerned.