Just because you can build a microchip doesn't mean you can build a spaceship and vice versa.
So I'm not surprised about that they e.g. left out generics and said they did so because they didn't know a good or right way to add them to the language. They were honest at least which I value a lot.
As to the success of Go that you mention. Well, let's be honest: it targets junior developers, or at least that was originally a major goal. It is backed by Google and is marketed.
There are just currently way more junior developers due to the demand and the developement of the field.
However, you can already see that a lot of junior developers that started with Go are not so junior anymore and now that they got more experienced, they demand language features that make them more productive - like generics. And they will be added and in the end Go will be a language that is not simple anymore, it will be the new python.
Go is a very practical and pragmatic language, no doubt. It's one if its strengths. But it is not by any means an advanced high-level language in any sense that I would know of.