Oh dear God, never use Kakashi as a means to compare Minato to. Its an insult to Minato. Just because Minato hasn't faced a Uchiha (that we know of), doesn't mean he doesn't know their abilities. That was proven when C knew what the Mangekyou Sharingan is and Amaterasu. Now, C wasn't even from the Uchiha's village. I think it is safe to say that Minato knows more about the history of his village than C does.
And if you use your "assumption" argument, just know you assume the same I do, you just go in the opposite direction.