Agreed - we'd probably all be most productive working in a language we'd designed ourselves, irrespective of the merits or demerits of that language for other programmers.
Yeah, but not everybody designs a language. Right?
[1]The usage of a language directly depends on comfort, productivity and efficiency.
Maybe ''Pike's language'' was a factor, but all the above relations[1] come true in wider light.
I'm not bashing Go here, just to clarify - I'm just saying that given Rob Pike's deep knowledge of the language and its libraries, and his heavy design input to it, it doesn't mean much that he's productive in it (well, besides the implied statement that he thinks it's not a toy language any more).
