I genuinely can't tell whether the article is suggesting that Inbox is for advanced users or for non-advanced users (and GMail for whatever the other user is). I believe, based on my own understanding of the two products, that GMail will continue to exist for advanced users, and Inbox will be simplified. But, the article is not at all clear on that; the last sentence seems to flip the meaning of the rest of the article and indicate that Inbox is the "advanced" one, while GMail will be made more simple. Or something.

Author can't English good.