> Even if HTMX makes the easy things slightly easier, is that worth investing time and energy into learning it in addition to those tools that scale up better?

Depends what your aim is. Do you want to become a full time front end engineer? Then no, probably focus on other frameworks. But do you, from time to time, want to put small pieces of interactivity on web pages when it isn’t the sole (or even major) focus of your job? Htmx might be ideal.