Full disclaimer.
I don’t know eruvin. Knowing eruvin means having learned well every Gemara with Rashi Tosafos and the Rosh. And then retaning near instant recall on every pertinent point. That is the standard I was taught in yeshiva to know a mesechta. I have never seriously learnt the topic, though I have read plenty of Iggros Moshe. It would only be fair to first learn the teshuvos that immediately preceded him to know what standard ideas he was coming from. I could argue what Rav Moshe says. But not what he holds. Which cannot be deduced from his teshuvos alone. And anyone who only throws around one line from two dozen teshuvos, is a fraud.
Such a fraud probably knows that Rav Moshe’s talmidim all say he never published exactly how to measure the 600,000 (Or any number.) for reshus harrabim linyan Shabbos.