When a new user has a better command of vi basics and gets a better grasp on the actual limits of Vim's built-in behaviour, and has invested some time in crafting a configuration that suits them, personally, very well for their work and workflow they have, then they're in a much better position to select plugins judiciously and don't have to use a configuration they don't actually understand.
So far, everyone who's recommended Janus to me or asked me to write about it turned out to have a pretty poor understanding of vi-like editors in general.
For perspective, I see the oh-my-zsh [2] project much the same way. I firmly believe that it really is better to start from scratch so that you force yourself to develop an understanding of the applications you use.
Learning vanilla vi has a slightly less obvious side benefit, too -- it works everywhere. You can log into pretty much any Unix-like system and type vi, and something understandable will happen. POSIX [3] is intended to ensure that.
[1]: http://vimuniversity.com/samples/your-first-vimrc-should-be-...
[2]: https://github.com/robbyrussell/oh-my-zsh
[3]: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/vi...