DY – Thank you. I respect your opinion as quite educated and levelheaded, so I consider your attention a compliment.
Nevertheless, I disagree with your corrections.
In Sefer Chazon Ish (although I can’t provide a Mareh Makom, as it’s been so long since I saw it), the same logic relied upon by Rav Moshe is presented. It is possible that the Ch’I didn’t want to rely on this Lma’aseh, which explains why he only allowed milk with the P’Ch, but he does use the Sevara.
Similarly, in constructing the Paris Eiruv, the Chazon Ish also did not rely on his own leniency. This interesting historical footnote notwithstanding, his Sevara is an important part of most municipal Eiruvin today.
Butter doesn’t need supervision because we know by process of elimination that it must be kosher milk; Chalav Stam is an extension of the same principle.
I don’t remember Rav Moshe saying to Kasher Keilim – Can you provide a reference?