Maybe the causality goes the other way: once you need to do something more complex than the basics, HTMX doesn’t work that well anymore

This has been my experience, the reality is HTMX doesn't scale well in terms of complex ideas / code. Great if you have something simple to achieve, not so great for a massive ongoing project.

In other words: It has a steeper complexity gradient, albeit with a lower complexity floor.

Though, for me, that begs the question: why not just use vanilla Javascript's .fetch()? One gets more flexibility than HTMX could ever provide, and the same logic is really not that many more lines to type.

99% of websites are, or should be, just a simple document(s) with a couple of forms, and the goal of HTMX is to help achieving low to medium complexity interactivity, and better UX on such sites easy. These are not the flashiest and most sexy demos, but the staple of the Internet.

If you really need to make a web _application_ with lots of reactive interdependent elements, HTMX is not the tool for the job.

HTMX is 14 kb of Javascript and additional complexity on the backend.

At this point you're better off using something like SolidStart

I feel like part of the mess of modern web development is the idea that most people actually need to "do something more complex than the basics". So much rehashing and effort spent trying to force MPAs into a SPA shape just because it's trendy.