“Rav Moshe was mattir on peanut oil for Pesach. Do those who cite him on eruvim also argue for peanut oil?”
By this logic, nobody can ever cite anyone. There are a handful of well-known cases where the American community breaks from the trend and does not follow Reb Moshe’s psak (eg. peanuts on pesach, shabbos timers, arba kosos davka being wine).
The minhag of most, but not all, of the frum tzibbur is to follow Reb Moshe’s psak regarding the Brooklyn eiruvin. In Manhattan, the entirety of the frum, non-MO tzibbur follows his psak regarding the eiruv.
Yes, we know there are those that are matir Brooklyn eiruvs. The discussion here is that the OP seems to be suggesting that even those of us who don’t should change our shittah due to some new change in metzius that he has been suspiciously unable to specify with a halachic source. Is it possible that this situation happened? Sure. Brooklyn could be deserted like Gary Indiana and no longer be a reshus harabim according to anyone, but I see no evidence that anything like that happened.