This makes sense, and when I first started writing Go, I felt the same way, but almost four years later, concurrency is one of the least important reasons I still write Go.
I wouldn't say all Gophers feel this way, but I know it's a very common experience for Gophers - "you come for the concurrency, but stay for the interfaces"[0].
[0] I've alternatively heard things like "readability", "tooling", and "robustness" used in the place of "interfaces" in this quote.
Yup. I literally just gave a talk at two Go conferences in the last two weeks (GopherCon India and GopherCon Dubai) about the io.Reader/io.Writer interfaces specifically. They're deceptively simple on the surface, but they're insanely powerful once you 'get' them.
There was a blog post a while ago about how golangs's interfaces caused issues in production because they're implicit.
Check out type classes for a superior way to solve this issue (e.g. what Scala or Rust do).