Berliner,
I cannot name a Rosh Yeshiva or “popular” Rosh Mesivta who was a product of YGMH. This doesn’t mean they don’t exist but I don’t know who they are. I don’t personally know many people who went the Yeshiva under the age of 40 and it is extremely unlikely to be either of those things at such a young age (unless you married in).
I do know, however, that many of the members of my shiur and the shiurim 2 to 6 years ahead of me were among the best bochurim and later yungerleit in the many world class yeshivas they attended after Montreal. They were among the very best bochurim in South Fallsburg, in Mir Yerushaliyim, in Lakewood etc.
Frankly I have never come across such a high percentage of top learners from one high school, as what I experienced in my years in YGMH. I am certain that within the next 10 years some of them will be well known as Rosh Yeshiva or “popular” and “distinguished” Ramim.