It’s very likely that the earlier meforshim had some kind of ruach hakodesh. (This is definitely true of Rashi)The more modern meforshim and mussar sefarim based their hashkafah on the earlier meforshim.
Either way, shiv’im panim l’torah. Torah doesn’t only exist for people to follow. It’s there to be discussed and questioned.
Even if there isn’t any “concrete proof”, there is proof enough that they are ethics we should follow because these people represented Torah and lived through torah in all aspects of their lives. Therefore, we can assume their ethics are the torah’s ethics as well.