“how many actually became gedolei hador in the past 30 years?”
Mass producing gedolei hador by age 50 or so (assuming bochur is in early 20s when he started to learn there) is a pretty high standard for any yeshiva, don’t you think?
I can think of several talmidei chachamim and roshei yeshiva/kollel who have learned in the Mir in the past 30 years though.