Including having proper slices, but not even one of the language authors was able to change WG14 mind on the matter.

That is what happens to languages that leave their authors behind and embrace design by committee.

Yes, but the language itself is OK-ish besides a pre-processor that's too skinny.

Standardizing libraries is one thing I really favor. But force fitting them into the language itself maybe like over-engineering.

Let me have an example. qsort() and bsearch() are powerful but the call/return overhead is really unbearable. A (much) more powerful pre-processor which is really part of the language (and maybe syntax-aware) could help in creating templates that would generate solid code for either function with the bare minimum overhead.

I am not saying like C++ templates, but like C++ templates.

I’m interested in that, do you happen to have a link or reference to that discussion?

This has the old days, what exists is Dennis's fat pointers proposal.

https://www.bell-labs.com/usr/dmr/www/vararray.html