Well at least in the case of Bg3 MC, you can't know for sure since you never played the full game. Who knows maybe by the end of the game you discover the MC has a crazy and amazing backstory that you only discover in the final hours of the game. Does that retroactively make him a good MC? Sure. Does that mean the companions deference to him throughout the game suddenly make sense? No.
I mostly agree with you except BG1’s MC was interesting from the start :b