I agreed with your one liner and agree even more with your expanded explanation!
The term developer is so broad, so overloaded, and will only keep getting more overloaded as the tech industry continues to expand.
If I meet someone at a party and they say they're a developer, even as a developer myself I have no idea what that really means, and I have to ask more questions and probably drill down for at least a couple more minutes before I have the slightest clue what their actual specialty and interests are, let alone what they do or are capable of doing day to day.
In such a specialised world, there's not really much sense in reserving any particular word for any particular category of job or skill, because to do so would be so high level as to be almost useless anyway. High level titles in this world are completely, utterly meaningless because people can and do use them liberally. We're in a place now where it's necessary to have a fairly involved discussion with someone to figure out what their real job and skillset actually are, whereas maybe 50 or more years ago, that perhaps wasn't so much the case. That's a very good thing and we should embrace it and not worry about broad definitions being 'misused'.
Put it this way, if I was being interviewed by somebody who wanted a custom web app building, and they genuinely confused someone advertising themselves as a WordPress developer with a full stack web developer, to an extent that it caused me not to be hired, I think that would ultimately be a positive thing as I'd almost certainly not want to work on that project anyway! There is no danger of the market for custom software becoming confused with the market for WordPress sites, and if there is an overlap, you don't, as a 'real developer' (air quotes very much emphasised) really want to be there anyway, right?