I'm not really going to argue on this any more, as I've articulated this ad nauseum elsewhere, except to say that, as with most people who argue for the existence of a distinct "Vulgar Latin", you are making a category error in defining "Literary Latin" is a living entity.

I have no idea what it means for a language to be "alive". That it's actively used? That it undergoes changes over time? Both seem to be true for literary Latin in antiquity and the Middle Ages.

"Literary Latin" is a construct that, from its inception, did not reflect the state of majority spoken Latin; conceptions of it rely on an idealized version of the language that demonstrably never existed as such.

The idea that Literary Latin has an "inception" seems incredibly strange to me - like at some point people sat down to create a new register? No, the Late Republican authors were imbued with an elevated register of Latin through their predecessors (Ennius, the annalists, senate decrees, ...) which they continued to develop (and if you look at the speech fragments of Cato censor, you'll be surprised how Ciceronian they seem in style). Formal settings require formalized language and if you dropped me into the early republic and the language used in religious rites or e.g. in the recounting of family history at banquets was the same spoken in the streets I'd be very surprised.

I don't know how you can claim that something "demonstrably never existed" which we hold in our hands (and if you are talking about the concept rather than the actual writings - all the grammarians you so easily dismiss attest to that). And no, of course "literary Latin" didn't reflect the state of the majority of spoken Latin - but it was spoken by some, was generally comprehensible to speakers of Latin and was regularly used in public settings (e.g. we see that Cicero tones down his style a bit when addressing the contio as opposed to the senate - as befits the difference in dignity - but he still very much stays within the literary register). A not inconsiderable part of my frustration is that you seem dead-set on reviving Bruni who I had hoped we had buried for good in the 15th century - where he belongs.

Does it represent stylistic trends? Sure. But these aren't nearly so standardized as is usually claimed, and obviously are linked to a very specific band of elite speakers.

At this point I have no idea what is "usually" claimed because the broad stylistic (and especially in the Late Republic also morphological and grammatical) variety in literary Latin is obvious to the eye. And, yes, those that shape it by becoming targets of future imitation are a very specific band elite speakers. Yet, this also is the language used in schools all over the empire when Vergil is read or declamation is taught and as such local elites everywhere can be expected to have been competent in it (without leaving much of a trace on it).

Nor is the "Attic" dialect represented by the dialect found in extant literary texts

Captain Obvious strikes again. Of course "Attic", "Doric", "Aeolic", ... refer to literary dialects (unless one specifies otherwise), not to the state of the language that was commonly spoken in those regions at any point of time.

but even for those who could speak it fluently it was a still a dead language, as it reflected an artificial, constructed usage.

That it is "artificial" and "constructed" doesn't make it any less real. But I guess now we have at least some criterion for when to call a language "dead" - except that literary dialects and elite sociolects everywhere reflect "artificial, constructed usages" which doesn't preclude them from evolving - when I write an essay or give a formal presentation in my native language (German) I do of course not use the language as it is spoken in the streets but do (with great lexical leeway) aim for an idealized version of the way it was written 80-120 years ago (e.g. Kästner is generally regarded as a good model of purity). And if I had children I would try to feed some of these (anachronistic, artificial, constructed, what have you) features into their everyday usage because they fulfill an important function as a social marker (e.g. the subjunctive in indirect speech has almost completely dropped out of common usage and can as such now serve to distinguish the litterati from those that are not; some genitive functions are becoming usurped by prepositional phrases, not following that development does not serve to distinguish you but is regarded as a baseline requirement in the academic world). But of course a hundred years ago, different standards would have applied regarding which language models to imitate when you want to distinguish yourself.

If you are actually interested in this question, there is lots of literature on it; see in particular Adams Social Variation in Latin Language for detailed responses to most of your claims about Latin register and usage.

Thanks for the recommendation. I'll check this book out later today.