The Rambam is stringent on פת בעל הבית not פת פלתר!
Are you saying this based on his “Yesh Mekomos” in Ma’achalos Asuros 17:12? It would appear that his psak in 17:9 is inclusive of this yesh mekomos and in fact he holds pas palter is assur.
Even a layman knows of this פרי חדש but also knows that it wasn't widely accepted. If you have a large amount of poskim agreeing to רדב׳׳ז והפר׳׳ח you may want to just post the מ׳׳מ here to make that case.
Pri Toar and Pri Chodesh write explicitly that they ate Chalav Akum based on the heter. The Steipler in Kreina D’igrisa says the Chazon Ish (who writes lehokel based on the Pri Chodosh) was matir CS during the war based on this. Many poskim write similarly, in fact R’ Moshe gave two reasons lehokel, one (mirsas) like the Pri Chodosh and only in the other one (anan sahadi) does he say even the Chasam Sofer would agree with his logic. It appears it was based on location, some communities accepted it and some didn’t (Sdei Chemed and Darkei Teshuva list communities that didn’t accept it).
Just came here to post that according to this ערוך השלחן being makpid on CY during עשי׳׳ת can actually be problematic, since most poskim actually do agree that it's NOT just a chumra, it's assur מעיקר הדין and they did not accept Reb Moshe's Kula, in particular בדעת החת׳׳ס that it was נאסר במנין בכל מקום ובכל זמן.
R' Tendler saying it's just a chumra is irrelevant as he probably wasn't giving any validity to the majority of poskim who were opposing his shver's psak.
This would create an interesting situation that those who rely on Reb Moshe should not be machmir on עשי׳׳ת with CY, but we gotta get a clear ruling first if we go by this ערוך השלחן that whenever there is a מחלוקת הפוסקים מדינא one should not be machmir on עשי׳׳ת. It seems to be a big chidush.
In fact the Aruch Hashulchan is one of the major poskim who hold like the Chasam Sofer (along with the Chochmas Adam) although he has somewhat different reasoning. He brings down a story about a fellow from his community who, relying on the fact that there were no non kosher animals milked locally, was served milk mixed with animal brains, and exhorts people to be careful with divrei Chazal.
As to your point- the Chasam Sofer makes mention of this in his famous psak where he says Chalav Stam is totally assur afilu batul ta’am lo batul gezeira. He makes note of the fact that most of Kehilas Ashkenaz is (was then) noheg lehachmir, and says if you hold like him it’s assur derabanan and sfeiko lekula, but if are in Kehilas Ashkenaz and you hold like the Pri Chadash it’s considered a neder and it’s assur min hatorah so sfeiko lechumra! (I just want to point out though that several friends of mine learned by R’ Nota Greenblatt in Tennessee and he told them beshem R’ Moshe they don’t need to be matir neder to drink CS in Memphis as their whole hakpada on CY was based on the fact that they live in town).
I have heard some opine that R’ Moshe was giving an after the fact heter based on the observable fact that most Americans drank CS, and therefore it was minhag hamakom to rely on the PC.
What a letdown. 
When you're ready, please start a new thread for this (unless there's an existing thread for CY/CS already).
If you’d like I can try to write up a basic summary of CY- from the Gemara down to modern day poskim based on the Shivti marei mekomos. It’s a relatively short contained sugya.
