To make the 16 supporters of the Manhattan Eiruv into rov against the 5, they would have to be disagreeing on one specific reason (besides for other factors). Rov poskim is still a din of rov.
I’m not really interested in debating what rov poskim is or isn’t. There have been hundreds of dissertations on this topic. And I don’t know why you mentioned the Manhattan Eiruv from sixty years ago. It’s not up anymore.