Except you also fell for the trap of pretending to be educated. The entire "how to use 'octopus' as a plural noun" is an internet clickbait phenomenon, and both linguists and communications experts have chimed in to say that language is not prescriptive based on supposed origins of words/phrases, but rather it is labile and the most correct form of communication is that which is most readily understood -- therefore, they agree, saying simply 'octopus' or 'octopuses' is correct in English, as that is what English speakers already use.
A word becomes distinct from its origins based on the context it is used in - i.e. we're speaking English in the modern era, derived from generations of English speakers, and we are so far detached from any Greek origins in our language that it may as well not exist; these words have become English words through common use, and thus are subject to the grammatical rules of English. In the future, other words of varying origins with their 'appropriate' pluralizations and conjugations may be slowly overwritten by casual or undereducated use, adopting English grammar instead, and as long as that becomes the most common use, it is then the correct one.
After all, language is for communication, and communication requires common understanding, so language is naturally defined by that which facilitates communication - not notions of history or propriety.