[foldr]

Which proposal would you rather had been adopted instead?

It's strange to describe the current implementation has "half thought". A lot of work was done to make sure it was correct: https://arxiv.org/pdf/2005.11710.pdf It's probably one of the most carefully thought through generics implementations in a mainstream programming language.

>It's not rocket science, there are 100s of languages with Generics, including languages with many orders of magnitude more than the adoption Go has.

It's easy to add generics but not so easy to get it right (see e.g. Java's soundness issues, the total mess of C++ templates). Rust's generics also have some dark corners (e.g. https://github.com/rust-lang/rust/issues/84857).