libstdc++'s <print> is very heavy, reflection or not. AFAIK there is no inherent reason for it to be that heavy, fmtlib compiles faster.

<meta> is another question, it depends on string_view, vector, and possibly other parts. Maybe it's possible to make it leaner with more selective internal deps.

I don't know the exact details, but I have heard (on C++ Weekly, I believe) that it offers some advantages when linking code compiled with different compiler versions. That said, I normally avoid it and use fmtlib to avoid the extra compile time. So it isn't clear if it is a win to me. Header-only libraries are great on small projects, but on large codebases with 1000's of files, it really hits you.