The letter in chelek ches was written to a yeshiva, not for the general public.
It’s not written for a yeshiva, it’s written for a community.
As for a Rav who disagrees with R’ Forst, I already named one – R’ Dovid Feinstein.
You’re switching arguments here. You asserted that R’ Moshe did not intend for that teshuva to be printed, and your proof was that it was not in Igros. I asserted that the essential point was made in Igros as well, and that it is illogical to assume that R’ Moshe wished to “hide” his opinion that one should only rely on his heter b’shaas had’chak. I proved my view by pointing out that R’ Forst, who printed that teshuva, feels that R’ Moshe had no problem with it being publicized. Now you say that R’ Dovid disagrees with R’ Forst. Where is there any sort of evidence that R’ Dovid thinks that this particular teshuva is supposed to be a secret?