> The same way in that a CS PHD is going to be able to pickup programming languages better and more quickly than someone who has learned C++ and python, they understand the underlying mechanics of language, what makes it work.
... have you ever actually met anyone who got a PhD in CS? Because first off, very few people will actually study the "mechanics of language" in doing a CS PhD. If you're studying compilers or formal methods or maybe software engineering, sure, you'll study up on programming language semantics; but if you're learning AI or operating systems or computer architecture, you're very unlikely to touch those semantics. But even assuming you have someone who has actually taken those graduate-level courses (and I have!), it's not actually helpful for learning new languages. Learning semantics is essentially learning how to give meaning to the expression "a + b" (there are many ways to do this, and they have different tradeoffs), but if you want to learn a language, all you really want to learn is that "a + b" adds two numbers together, let's move on.
There's a similar gap between learning languages and being a linguist. As I understand it, most linguists are not polyglots (actually, I think a majority of them may be monolingual!), and most polyglots are not linguists. The linguist is the person who will tell you that English doesn't have a future tense: instead, you indicate the future by using specific helping verbs in the present tense. Anyone instructing English as a second language will slap the linguist on the head for being an idiot and tell you that the future tense in English is the "will X" construction.