Well, sorta kinda.
Scholars didn't so much invent the concept as describe what was happening. True enough, the term 'modal verb' may not have existed but that word that was the modal verb did. Grammar is rule driven, it's true, but scholars only identified the rules rather than invented them.
Where people can get a bit bent out of shape is in thinking that those rules are set in stone, cannot be messed with, when they're only really convention. We've kind of agreed them amongst ourselves, in an unstated fashion, to facilitate understanding. They've never been rules as such. We tend to know what they are (and hear the 'clang' when they subverted) without being formally taught them. Languages are continually changing, those conventions change (and are different in different languages/dialects/accents anyway) and so, imho, attempting to anchor down those conventions (and call them prescriptive grammar rules) is a gesture in futility.
That all said, it is (imho again) a wise person that realises the effect of that language clang I mentioned. There are times when it is perhaps in your own best interest to become multilingual and adopt the appropriate form. We do it naturally anyway (in courts of law, with the inlaws, whatever) so it's only an extension of that. Linguists call it accomodation. It may not be 'right' to have to tone down your much loved accent, with all it's idiosyncratic grammar features etc, for a job interview or whatever - but that's up to you to weigh up at the time.
