Become great in language X seems the wrong goal to me. An enormous amount of things and at the same time the most important things that make you a great software developer are completely language agnostic. And I would argue they are harder to learn through the lens of a single language and software stack. You then still have to become a productive software developer knowing your libraries and tools and their quirks but this seems secondary to me and easily compensated by your favorite search engine. Or by example - knowing when to use a set as opposed to a list is more important than knowing in which namespace you can find the implementations for language X.
