Daas Yochid
“R’ Moshe ZT”L is matir all milk based on that reasoning;”
thats perfectly fine. i dont take exception to being matir all CS. i am pointing out though, using that reasoning (like R’ Moshe) you have to be matir ALL CS; it doesnt make sense — to use THAT reason — and say only powdered is okay. iow, if you are machmir on CY only, that reasoning doesnt help you be meikel on powder. (it would only make sense if you are meikel on all of CS, if you go with that reasoning.)
“He maintains, though, that powdered milk was not part of the g’zeira.”
where does he say it wasnt part of the g’zeira? like charliehall pointed out, powdered milk didnt exist at the time of Chazal. so when Chazal made the g’zeira they never excluded powdered milk.