He knows almost nothing about MC I'd imagine. They come from a family line of warriors, I think its totally normal to want to test out your future son in law if he can protect his future wife aka his daughter from assassins and other killers who have been trying to kill you your whole life and will now also go after your future wife. Like typical muscle heads the Sword speaks louder then words.
also another part is I think that the only reason MC was able to hit the dad was not only because of smartness to hit the sword in the same spot/the perseverance to keep going because he loves his girl BUT the main reason being that the dude has been abused his whole life so I believe that he can TAKE the dmg inflicted to him that most people wouldn't.
"I know nothing about him so I'll beat him up to the point that he has wounds all over his body".
No I don't see how that'd make him any less of a psycho, and who wants to marry a wife with a psycho dad that might beat you bloody over who knows what reasoning.
FL should really be much angrier than she is for this nonsense.
Testing for power to fight against assassins while it makes sense in the normal manga isekai, it's obviously absurd for a noble. MCs experience should not be seen as a standard...
But rather than just how absurd it is, it's not like there's a time limit of 1 hour to test his future son in law, there is no reason to pummel someone into unconsciousness just to find some "potential to protect".
I'd even say that without actually trying to teach him anything there's no way to judge such a thing, since hes untrained.
Speaking of being untrained, since he could grow up untrained, obviously it's not a requirement of being a noble to fight off assassins and shit, this world is not a battle manga where nobles are the highest combat force, losing their title if they are too weak right?
We also do not know if hes marrying into her family or if they are forming a dukedom or what's going on with that, hes a fucking prince after all.
Having a past of pain and abuse does not actually make you fine with being hurt... But well to each their own I guess.
Or are you talking purely physically? Since he did it yes, obviously he can do it, but emotionally that's still unacceptable for anyone with some measure of self worth (MCs obviously has none).