Not even close, and I am a fan of abseil. The design of abseil has legacy constraints that don’t need to apply to a C++20 clean room implementation. I have better re-implementations of abseil components in my own “standard” library simply because I didn’t have those constraints.

There are many good libraries out there, or fragments of libraries, but I’ve never found one that really scratches this itch.

Could you give a couple examples?

Of libraries that are better than the STL? Or data structures that the STL is missing? Without getting into the weeds of esoteric data structures and algorithms I think there's a few holes that aren't addressed:

https://github.com/martinus/unordered_dense provides better replacements for unordered_map/set.

The STL is missing B-trees and B-heaps, as well as d-heaps.

STL is also missing a radix sort, which is even more sorely missed now that we have std::executor::par_unseq to play with.

Examples of better design than abseil in a pure C++20 implementation