Arrays and slices really have nothing to do with generic programming. Java has poor generic support (type erasure) and C++ has poor syntax and a bad design for iterators. Languages with decent generics support have none of these problems.
If this is 'armchair criticism' why do Go's designers say they are considering adding generics support?
It's actually clearer as to what's going on since slices are a language primitive. They are simple and extremely transparent. This is absolutely not the case with Java's collections library or the C++ STL.
It wouldn't be a trade-off if there weren't situations where generics are really useful. But this rings more like an armchair criticism of Go than a criticism from someone who's written some Go programs. For my part, I wish languages like Java were less hostile to arrays.