If you really want to be pedantic, "from hoi polloi" is incorrect, because it does not use the correct Greek declension to go with a "from" preposition.
The normal thing to do in that case is to ignore the parts that are just artifacts of the other language, so you'd say "the polloi". (Or, really, you'd say "the many"; it's not an esoteric concept.)
If you read older translations of mythology, you'll see that inflectional endings for foreign nouns are just left off, so you have e.g. Jormungand instead of Jormungandr and Thor instead of Thorr. (It's true for history too, where we prefer Virgil to Vergilius and Ovid to Ovidius.) Recently there's been some kind of fetish for including foreign artifacts in borrowed words, even when those words are already well established without them.
I kind of get the sense that this kind of thing is driven by people who think that learning a foreign alphabet is the same thing as learning a foreign language.
"The hoi polloi" is a fixed phrase in English. Its etymology is irrelevant. We don't pronounce it "properly" either. Thay is because it isn't Greek! It is English. It has Greek origins but it was long ago borrowed into English and now follows English rules. ~Everyone knows "hoi" means "the" in Greek. But the phrase in English is "the hoi polloi". It is never found except as "the hoi polloi". If you said "Hoi polloi are upset" in real life people would look at you funny. There are loads of other examples of this happening. For example there are various verbs and adjectives from Latin that have been borrowed as nouns into English. If you go "uhm actually that is a verb in Latin actually" you are annoying and wrong. Language evolves.
Showing off your education is oftentimes used to signal high status. That often fails. You can of course argue with the OED:
Hoi is the Greek word for the, and the phrase hoi polloi means ‘the many.’ This has led some traditionalists to insist that hoi polloi should not be used in English with the, since that would be to state the word the twice. But, once established in English, expressions such as hoi polloi are typically treated as fixed units and are subject to the rules and conventions of English.
Disclaimer: I'm one of the οἱ ὀλίγοι from the colonies, so the only thing I was learnt is baaaaaaa.
Fellow Kiwi? The tone of your comment makes it sound to me like you disagree with me but I agree with everything you are saying.
I am usually a traditionalist but on this one I think the tradition to follow is the English one. I prefer the traditional English pronunciation of Latin (so "caveat" is "kay-vee-it"). Hell, I would prefer if we still nativised foreign loanwords and names: Saint Peter wasn't called "Peter" obviously, but I don't speak Greek or Aramaic or whatever. Peking isn't what the Chinese call it but neither is "Bayzhing" which is how English people pronounce Beijing, and so on. Plus now "Peking duck" doesn't make any sense...
hoi polloi was borrowed into english as a way not only of saying "the masses", but of signalling one's own status above the masses. Another way of signalling such status is to show off one's deeper familiearity with obscure details of foreign languages.
or to put it another way, only hoi polloi say "the hoi polloi"; on this same topic linguists are generally incoherent, so intent are they to repeat yet again "descriptivism doncha know"
I'm aware of that, but it is not typical of borrowed terms. You can't explain the oddity of the phrase by appealing to the idea that that's how foreign terms are borrowed into English, because it isn't.
"hoi" means "the" in greek. So, if you want to set yourself off from hoi polloi, don't include the "the"