Almost all of the gaonim that came out of the pre war yeshivos were against the eiruv in Manhattan. Some were even older than Rav Moshe. Their opinions are published in their seforim. Or can be found in their notes. They mostly thought that allowing an eiruv in such a metropolis is a chiddush. I didn’t mention the kol korei.
The Boro Park Eiruv features many poskim of little renown. They had dozens of peers that were still in kollel. I don’t think such would count as rov poskim. It’s not bechachma or bminyan. It was not in my mind to belittle them CH”V. Mostly they signed to announce to their peers that they felt ready and able to defend the eiruv.
I don’t go care for either KK. I just posted because you mentioned something like rov poskim.