"Newbie distro" is usually meant to describe an operating system that is easy to get into for newcomers to Linux, who don't want to get into the details yet and just start using it. This is my interpretation of what the communities usually mean by that term.

If you like Mint, then there is no reason to switch off it, especially not for the reasons because people call it "newbie". It's likely that there is no "better" distribution for you and everything that is different will be bother you. One reason why you might want to switch off could be a Rolling Release model, like Archlinux (or something based on Arch that is rolling too). But that comes with its own problems and you might not like it to have an ever changing and evolving system, always updating to the newest. If that doesn't excite you, then maybe you should stick with a cyclic release model like Mint. And nothing wrong with it, if you like that stability*!

*stability=here that doesn't mean a stable system in sense of problems, but more in the sense of non changing stable environment, unstable would mean its always evolving as a rolling release, not that it is less stable in problems