Vulgar Latin — real or not?

By "Vulgar Latin", I mean the colloquial version of the Latin language that non-elite sectors of ancient Roman society used in contrast to the speech of the upper class, the version that gave rise to the Romance languages.

I watched a video on YouTube by Luke Ranieri of polyMATHY that argued for the non-existence of "Vulgar Latin" because he doesn't find the term useful for describing colloquial registers of the Latin language through the years.

He basically said that what we tend to call "Vulgar Latin" are actually informal versions of the stages of the Latin language.

I'd like to hear your insights about this.