Yes, Go has very bad primitives whichever way you look at them. I still think you can't say a language with built-in immutability is more boring technology than one with built-in mutability.

There's nothing stopping you from using Go's maps without mutation. You can go ahead and send copies of maps through channels, just like you would if they were really immutable. Sure, the interface is clunky, but so is every other interface in Go, so I don't see too much reason to complain here...