Htmx advantage is not that it sends less bytes, but that it effectively removes frontend. Getting rid of the frontend dependencies, builds systems, and languages can bring a lot of speed to a project.

Of course the downside is everything must go to the server. While not perfect, many spa also do not work nicely without a connection, although they could.

Another thing is that the templates can get a bit crazy quick.

I found a good solution is to use swap-oop (https://htmx.org/attributes/hx-swap-oob/) for everything and have a "component" wrapper server-side to abstract the ids and which template to choose.

Then, some kind of typed data structure tracking all the element ids, since you need to refer to them from the templates to know which element to update. This way you can easily find all the templates that update a specific id or all the ids that are updated by a template.