I'll offer one here... using HTMX usually means you're going to be writing HTML templates, and HTML templating languages don't have much IDE support. I really miss goto-definition etc. when I'm writing Jinja templates.
That being said, I've personally found Rust/HTMX to be a magnificent combo. I personally find writing backend endpoints in Rust to be no more cumbersome than any other language (after becoming comfortable with Rust)... and there's massive gains from the incredible tooling and type system.
I wonder if you've considered using Askama for your templates? It has a Axum integration that cleans up some of the boilerplate around template rendering. There's also an open PR for block fragments [1], which will make componentization of HTML fragments much easier, as discussed in this essay on the HTMX site [2].
We need more projects like this to demonstrate how useful, highly-interactive apps are made with HTMX. I'd encourage skeptics to try the same before writing it off.
[1] https://github.com/djc/askama/pull/824 [2] https://htmx.org/essays/template-fragments/