Full agreement. Proc macros are an accident of history in many ways. I would encourage new language authors to go straight towards reflection instead.
Despite their definite flaws, though, I have to agree: compile-time code generation via annotation processing is something I think we should do more of (and invest more time into better tools for it).
I'm not exactly sure how you can really make this particular problem better when working with compile time code generation. But what I'd say WRT cleaner and clearer, Java and Kotlin both expose much higher level type information than is available in rust's proc macros. That's mostly what I meant by cleaner and clearer. Without needing to pull in weirdo not-quite-third-party libraries, you can reflect on and generate for all sort of different type information.
It seems to me that something like this should be possible with rust given its early transformation into high level bytecode. But I could see why the rust devs have pushed back on doing that as it'd really lock in features they might not want to lock in.