Personally, I would say that if you are doing DOM updates via AJAX calls that return HTML, HTMX is just the correct way to do it. (Unless you're using some other solution already for other reasons and it also includes that functionality.)
Sure, you could do the basics of that workflow with twenty lines of your own JS, and save a dependency. But that's the kind of thing that is generally very unscalable, because unless you're very disciplined it quickly becomes a mass of spaghetti. The virtue of HTMX is more in how it channels and limits your code, than in the new capabilities it grants you (which were all in common use as of 2005 or whatever).
Why is it better to render JSON on the server, read that JSON in a separate client app that you also have to write, and then do a bunch of manual DOM calls in Javascript, rather than rendering HTML on the server and letting the browser's blazing-fast compiled HTML parser turn it into DOM for you?
The cost of launch is small-ish compared to the total program cost, but the limitations on launch condition the engineering requirements in ways that inflate the engineering costs. JWST had to be built as an insane on-orbit autonomous origami project because its mirror couldn't fit in a fairing unfolded. Repeat for ten thousand other decisions that are made in order to optimize weight or volume.
If you can launch a hundred tons to orbit for $5M, you can just make a huge dumb cheap telescope and throw a dozen of them up there. Quantity covers a multitude of sins.
Sure, you could do the basics of that workflow with twenty lines of your own JS, and save a dependency. But that's the kind of thing that is generally very unscalable, because unless you're very disciplined it quickly becomes a mass of spaghetti. The virtue of HTMX is more in how it channels and limits your code, than in the new capabilities it grants you (which were all in common use as of 2005 or whatever).