“therefore I take the last few igrus moshe with a grain of salt”
Absolutely no question.
I’d say more than a grain. Though I wouldn’t say “complelty irrelevent”
in this case though we also have earlier teshuvos eg YD 3:176 written in 5736 (1976) published in chelek 6 which I dont think ANYONE has questioned the veracity of. wcich seems to support brain death
Plus R’ Dovid Y”blch supports this understanding of his father’s position