Well, we know how one talmid compared the Rayatz and Rav Aaron. Rav Aaron was very, very humble. Any real talmid of the R”Y zatzal has a real hard time criticizing anybody. Even those that deserve heaps of criticism. I’ve not heard them discuss Chabad much, but they all were very impressed once they met the Rebbe. Rav Belsky did tell me that the R”Y zatzal did not hold of the Rebbe. He quoted Rav Aaron about two other aspects of Chabad.
I did not say the Rebbe was able to learn like a Rosh Yeshiva. Rav Belsky had a very high bar for everything. Did you ever ask him if Rav Shach knew how to learn, or if he learned Rav Shach’s Torah?