I find it amusing that people would use the term "incompetence" to describe Ken Thompson and Rob Pike. These two guys have been as instrumental in shaping modern computing as Linus Torvalds, Bill Gates and Steve Jobs.
But I guess it's easy to be critical of other peoples output when you're an anonymous internet user yourself.
Sorry, I thought it was clear - incompetence regarding [modern] language design. They don't deny this neither. And it seems they're even proud of this.
I don't think your amended statement is much better. They have designed a language that meets their goals. They have decided not to include many things, but that does not mean that they are not aware of them, or are incompetent for doing so.
Or arrogance and incompetence. It's been said many times. Go team should spend at least one day with Gilad Bracha...