Eli lev: I don’t know why you think Reb Moshe was “very makpid” on chalav Yisroel. While he did take it on himself as a chumra, his son Reb Dovid says that he never served the children chalav Yisroel and even gave them ice cream that was chalav stam.
I’m also not sure where you saw that the “metzius” today is different than that described in Igros Moshe. He writes explicitly that even if the inspectors do not come regularly and do not check carefully it is still permitted to drink. It couldn’t have gotten much worse than he describes it.
By the way, I personally am makpid on chalav Yisroel. But I know it is a chumra and would not necessarily require it of others.