A common theme is that only languages that had generics retrofitted into them have awkward implementations (because your design space is now constrained), while those that were designed to have them ab initio typically work fine.

I don't really want to belabor the point of Go and generics; it's one of the many simplicity vs. expressiveness design choices that language designers have to make. But the claim that parametric polymorphism in a statically typed language is (presumably inherently) an awkward mess is a peculiar one, given that there are so many successful examples.