[SuperV1234]

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.

[bluGill]

The standard library shows the roots of the mid-1990s and there are a lot of things we would definitely do different today. However, it is still extremely well defined compared to most everything else. C++ is one of the few languages where the library actually guarantees how an algorithm works, which is both good and bad. The bad part is some things that made perfect sense in 1995 simply don't make sense in our modern CPUs where cache is important.