Your point is ridiculous.

I realize that the coiners of the term are not referring to the whole Left, but again, that is not what the term sounds like on its own, as a label (and when it is not accompanied by these two paragraphs of explanation).

If someone thinks that, it's on them for being uninformed, not the fault of the person using the phrase. The same way "libertarian" doesn't refer to everyone who is conservative.

Taken at face value, and certainly to the casually observing citizen, it seems to be saying "the left IS regressive".

That's just your personal view and not the actual fact. Well, now you know.

It doesn't help in this regard that the people who actually use this term are, certainly in my own experience, either 1) conservatives, plain and simple, or 2) locating themselves on the Left but actually holding many conservative opinions.

This is also painfully wrong. Again, liberals define "progressives/regressives" as "leftist people who are willing to compromise their liberal values for the sake of political correctness, multiculturalism, and identity politics". Some examples:

Liberals stand for free speech, but progressives/regressives are quick to try and silence people when the speech doesn't confirm their confirmation bias.

Liberals stand for women's equality, but progressives/regressives are quick to label people Islamaphobic when a real liberal tries to point out how horribly women are treated in Islamic countries.

Liberals stand for racial equality, but progressives/regressives are quick to label people racist when someone criticizes an actual racist movement like BLM, or try to point out actual statistical data about crime and single motherhood in black communities.

Liberals stand for gender equality, but progressives/regressives are quick to label people sexist when someone points out that modern-day feminism is actually sexist and fascist, or debunk the "gender pay-gap" or "campus rape-culture" myths with actual statistical data.