I have seen zero in the way of real-world maintainability data saying that it is true. Mind you, there is very little good real-world public maintainability data. And therefore I will say that, when I was at Google, I saw some of their private data, and it wasn't true there.

Specifically, most of the win from a type system is simply having one.

Mind you, the data that I saw includes some of the same data that informed the Go team's decisions. And therefore it is no surprise that it fits their ideas. Also that data was rather lacking on, say, real world examples of Hindley-Milner type systems. So maybe those actually work well in practice.

I also have reason to suspect that Rust's type system actually is a big win. Though I haven't seen actual data on it. But since Rust was in early development back when Go was started, it isn't a shock to me that Go didn't incorporate a lot of lessons from Rust.

So I am inclined to think that I'm basically right. However I would also classify my knowledge as only moderately well-informed. (But in a subject where I think that most people who chatter about it are essentially uninformed.)