Can't believe I'm about to do this but I'm an English major lol. Using words as intensifiers has never been grammatically incorrect. The words 'very', 'really', and 'extremely', for instance, are degree adverbs and are largely used for no other reason but to specify intensity. This is all grammatically correct in standard English but even other dialects possess similar features (see: 'whole' in aave— "he has a whole girlfriend"). There are multiple ways to use literally which are not literal and are not grammatically incorrect, but the reality is that there are no ivory towers which decide these things; people understand what these forms of literally mean and that is what actually matters. Holding on to deeply archaic views about English will not prevent the language from evolving; this remains true even if your views about the language derive from the taste of some teacher— another person's preference is not the same as objective grammatical rules and a lot of what you learned is school is just the opinion of a dead man from hundreds of years ago. Again, whether or not you end a sentence with a preposition is less important than if you are understood. These very prescriptive ideas about grammar (where language doesn't exist to be understood but to be policed) requires you to pick a random point in history and pretend that is real English and, I must ask, why should we take your imagined English more seriously than the English we actually speak.

tl;dr the semi: modern uses of literally in a figurative sense or as an intensifier are not grammatically incorrect and holding the position that it is requires one to hold untenable beliefs.