“Rav Moshe addresses the newly built Flatbush eruv that he hadn’t wanted to get involved in the project because there is many opinions on what is reshus harrabim and what is dalsos neulos and they can always consult the seforim instead of him. But once it was publicized that Rav Moshe was the one who permitted the eruv because of the previous sentence, he felt compelled to respond with his personal opinion as it was already laid out in his first teshuva.”
After trying to give a running commentary of Rav Moshe’s teshuvos, the fact that you leave out pertinent points demonstrates that you either don’t get it, or that you learn lekanter. E.g., you omitted that Rav Moshe did not want issue a p’sak din barrur, because he knew that he was mechudash, and was going against the poskim.
“4) Rav Moshe’s own opinion is clear from his first teshuvah.”
You are discombobulated. The teshuvah prior is regarding Manhattan (you cannot be referring to 1:138, since that has nothing to do with reshus harabbim). Rav Moshe needed to formulate, at this time, his opinion, since Manhattan’s metzious was unlike Brooklyn.