Clean Code is not bad in itself. The problem is that some people made it a bible, like the absolute truth (I guess it is written in that way), and that's where it fails.
let's hope generics doesn't become a over(ab)used feature, that'd make the code harder to read and my experience harder to maintain, especially because when you need to fix something it takes a lot of time getting in context so you can actually write the code for the fix.
I mostly write Go these days and haven't found many use cases where generics are needed but there are definitely cases where they would make the code nicer.
the HTTP benchmark is not fair since the crystal implementation is setting the content type explicitly while the Go implementation is auto detecting it.