Those signatures seem complicated to me because there's a pile of arguments and some of them are functions with extra annotations, not because there's generics involved. The equivalent signatures using interface{} (or maybe something more precise) would be likely just as noisy, if not more so.
Some people are turned away from C++ after seeing random bits of crazy language/template misuse, although when used sanely C++ could've served them nicely for their job.
Same thing is going to happen to Swift very soon.
https://engineering.kitchenstories.io/comfortable-api-reques...
Those function signatures are definitely not... self-documenting, I'd say.