This is, after all, how Thoughtworks make their money - they insert polyglot (read graduates/juniors with a smattering of experience in different languages) int

This is, after all, how Thoughtworks make their money - they insert polyglot (read graduates/juniors with a smattering of experience in different languages) into projects and bill for experienced professionals (the "seasoned" developers in this article). This article conflates "varied experience" with "good developer" and "seasoned developer" with "bad developer". In the real world, this is not the case. So whilst I agree with the premise that varied experience contributes to being a good developer and that polyglotism is very healthy and a positive sign, I disagree with the broad conclusions implied by this article.