Little Froggie croakth: he was once מכוין to a Tosfes’ Kasha
this is true. Unfortunately, I am not aware of well-developed widely appliable tests measuring learning knowledge and abilities. Maybe you know? “knows whole shas” and “gaon” are just too wide and subjective, especially in our Lake Wabegon times, when everyone is a Talmid Chacham above average.
You can go around, like I do, and ask people obscure questions and see who can answer it, but this is not scalable.
I am not the only one who is interested in being able to sort out this. R Soloveichik in early YU days laments that he is giving the same semicha to all students instead of giving them a grade. I presume he would answer when a congregation calls him and asks about a specific candidate, but he felt that transparent information would be more useful.