That’s funny, I was sure the Shulchan Aruch’s language in ??? was, “??? ???? ??? ????? ????? ?????? ??? ?? ??? ??? ???? ????? ???? ?????? ??? ?? ???? ?? ??? ????? ???? ???? ???? ?? ???? ????? ????? ????? ??? ???? ???? ?????? ????? ??? ???? ???? ?????? ??????”
I see twice that it says Seudah Shlishis. So it’s wonderful that you have “seforim” that give you lots of different inyonim to think about, but I highly doubt any of them reject the title “Seuda Shlishis”. The term Seudah Shlishis is also mentioned in the Rambam where he writes, “???? ????? ?????? ?? ????” if you want a rishon.
As far as your pronunciation quip re: Chazon Ish; Rav Elyashiv zt”l gave a psak that unless a person has a mesora to pronounce the cholam “oy” from previous generations it is incorrect to do so. While there are those that are cholek, I don’t think that leaves you any room to attack someone who doesn’t pronounce it “choilam”.
Gramatically, Oheves Yisroel is correct. In Yiddish/Hebrified English, it became acceptable to ignore grammar once a term is borrowed. To have complaints re: people who are makpid about grammar would be incorrect on your part – but it would be in line with the minhag, if you will, of many Americans.
You are correct, however, that in the context you mentioned, “nifteres” would be incorrect.
Edit: Ahh, my mistake. The Rambam and R’ Yosef Karo were Sefardim. Seudah Shlishit(h). Not Seudah Shlishis. Silly, silly me.