The question is whether something belong in the language or in a library (possibly the standard library).

A guiding principle of C++ is that if something can be implemented cleanly and efficiently in a library, the language should not be extended to support the use case.

Now boost.pfr is exceedingly clever, but relying on speculative pack expansions or using stateful metaprogramming hacks is not something I would call clean and efficient, so proper reflection is warranted.

I do worry about the compile time impact though.

the only thing that should be standardized are things that cannot be done through libraries in an efficient way. Boost.PFR is great, I built a lot of things on it, but eventually you hit the limits of what a pure library approach can do -> language feature.

By your logic we shouldn't ever use external libraries.

PFR has given us reflection since C++14.

I also don't think the Standard Library is particularly well-defined nor well-implemented, as demonstrated by the atrocious compilation times.