Joseph, I read the thread you posted. There’s a reason the mods closed it. I don’t know about the quote you provided from Mishnas Aharon, but even assuming it is being interpreted correctly, “MO” was prevalently used as an excuse for people who weren’t shomrei halacha (sadly, this still happens nowadays). Perhaps that is what Rav Aharon was referring to. Or maybe the quote is taken out of context/misinterpreted; I don’t know because I have never seen the sefer. Also, I have heard that some of Rav Kotler’s hespedim are purposefully omitted from Mishnas Rav Aharon, so I have my misgivings about it.
Please read my post. I have seen pictures of a) Rav Aharon with Rav Soloveitchik at a chinuch atzmai event which Rav Aharon invited Rav Soloveitchik to be the keynote speaker b) Rav Aharon’s son, Rav Schneur Kotler, walking with Rav Soloveitchik c) Rav Schneur, Rav Moshe Feinstein, and Rav Soloveitchik sitting together. I also have knowledge of d) Rav Moshe, Rav Feinstein, and Rav Soloveitchik “officiated” at a wedding (neither of them was the Mesader Kiddushin) e) The eyewitness story I mentioned above where Rav Soloveitchik’s respect for Rav Aharon was revealed and Rav Malkiel Kotler agreed that he should have been at Rav Soloveitchik’s funeral, but couldn’t f) Another eyewitness story where Rav Soloveitchik and Rav Aharon met discussing a halachic issue to which they radically opposed each other. Rav Aharon referred to Rav Soloveitchik as “Bostoner Rav” and Rav Soloveitchik called Rav Aharon “Kletsker Rosh Yeshiva” (note: and the chinuch atzmai event was not long AFTER this disagreement between Rav Aharon and Rav Soloveitchik). e) A talmid of Rav Soloveitchik who says that Rav Soloveitchik would call Rav Moshe Feinstein and Rav Aharon (and later, Rav Schneur) before a yom tov.
Do you have a source for your comment regarding Rav Schneur Kotler? If you want to throw around sourceless comments, I have also heard (not from an eyewitness) that Rav Schneur actually attended a shiur at YU for some time, so there.
There are also the posts of others, which I can not confirm, which say that many other gedolim respected Rav Soloveitchik while vehemently disagreeing with him. How? Because it’s a machlokes l’sheim shomayim.
I honestly don’t know what to say about Rav Elchonon’s letter. Maybe there was a different situation at YU than there is today, and kefirah was more easily accessible, or perhaps Rav Elchonon was misinformed about the situation (as we see with some gedolim today). I don’t know.