Feel free to call it that.

However, languages change with time. Even ones with formally prescribed rules do.

In most languages and cultures there's a tendency of speaking the "standard" dialect (or something close to it) in formal situations, and using a more relaxed form in everyday situations. English isn't like that - just look at anthing US politicians say - they don't strike me as using "formal" speech in the least.

There's also the distinction between "British" and "American" English. And I never heard a "whom" from an American ever, be it in real life or on TV, so to me it seems like an inherently "British" thing.

So appliying the rules "selectively" doesn't really bother me - especially when the incorrect way is so ubiquitous that it's more common than the pseudoprescribed way.

I'm content as long as the selectivity isn't dialed up so much that I need to use arm and leg gestures to communicate effectively.

Grammatical case. I can only really describe it in German. If you take the sentence "The boy gives the man the apple", it's "Der Junge gibt dem Mann den Apfel". "Der" is masculine form of "the" in the Nominative case. "Den" is the masculine form of "the" in the Accusative case. "Dem" is the masculine form of "the" in the Dative case. It's subject, indirect object, direct object, respectively, if you know verbs. There's also the Genitive case, which I didn't go into here.

The reason it's not sufficient to talk about subject, direct object, and indirect object though is because the grammatical case also goes beyond just a noun's relationship to a verb, it's also affected by prepositions. If you take the German sentence "I'm driving with the Man, but without the Apple" (I know, sort of a silly sentence), "ich fahre mit dem Mann, aber ohne den Apfel. The prepositions here, "mit" and "ohne", dictate that the two masculine nouns in the sentence get the masculine form of "the" in the Dative case and Accusative case, respectively. The reason why some prepositions dictate certain cases isn't clear to me. I just have the tables memorized :D

Grammar case (wikipedia)

Cases are a thing in languages with inflections such as Latin, Greek, German, slavic ones, and quite a few others. English used to have them in the middle ages, but they faded away in favour of prepositions, and the only place they still exist is who/whom.

Apparently he/him/his and she/her/hers are also inflections, but they seem different enough to not "feel" like inflections of the same root (especially she/her). Since inflections are not a common thing in English, one conceptually doesn't even know they aren't seperate words but deeply connected on a morphological level was opposed to particles (by, for, of, with). Especially someone without the context of knowing how they work in languages that utilize them on a more fundamental level.

However, looking at these words as if they're particles and not inflecions is a simple enough way to know how to use them (that's why you probably haven't heard of them).