Jothar,
Whilst I agree with your that a plain reading of the Igros Moshe shows Reb Moshe held cholov stam permissible bshas hadchak, I must say I’ve heard so many different versions of that story of someone in Reb Moshe’s family purportedly eating cholov stam, and on the other hand stories of Reb Moshe throwing up having found out something he ate was cholov stam… that, like you say, this is all hearsay possibly by people seeing what they thought/want to see.
You did say earlier you don’t know if Reb Dovid’s shitta is his own, or his interpretation of Reb Moshe’s.