Even without having concepts, a cpp compiler could conceivably detect at definition time that the template is acting as a generics declaration only, and treat it specially as if it was a "late-bound concept". That would potentially help with codegen, but it would certainly help with making compile errors better. I find it is hard to convince compiler engineers to divorce themselves from what the language semantics are and what the compiler does. As long as the user visible behavior is the same, you can internally handle things differently for conceptually this same feature.

Rust has the same problem as templates with macros. We haven't had a strong need to customize the macrosl evaluation much, but I could very much see us special casing macros that are function like, or have macro arms that can only be a handful of things in order treat them different so diagnostics get better. The only thing that comes to mind thar we do today, is that when a macro call falls through (no macro arm matches), we retry it adding commas in between expressions to see if it was just a typo.

Concepts could be much better, but first we only got the light version, and secondly the effort hasn't been there regarding improving the error messages.

Also, so far I would say they haven't been getting people rushing out to use them anyway, as C++20 is still too new for many projects.

Even GCC only now changed to C++20 as default mode.

Concepts have been disappointing for me: what they tell you is still buried in 1000 lines of errors.