Avira:
Are you talking about the new, 2022 Brooklyn eruv, or even the BP eiruv?
Even by your own admission on this thread, there were poskim who were Reb Moshe’s contemporaries who would approve of the BP eruv, albeit they might have outlived him. They surely always held it was mutar and just didn’t put it into action until later. As I remarked earlier, it does seem icky to wait until a gadol dies and then immediately start ignoring his psak, but I was told the same thing happened with the Forest Hills eruv. There was apparently a respected, European rabbi who kept blocking it as long as he lived.
My point being, maybe you could say it was disrespectful to build it, but at this point those rabbonim who hold it’s mutar will say so, and those who hold like them have on what to rely now. I don’t see any reason their shittah should be inherently pasul.