This article is well written, but it has nothing to do with mastering Vim. It goes no further than running "vimtutor" at the command line. It has all the same tips and shortcuts as any other vanilla Vim tutorial. This is a common problem among Vim articles and tutorials. Authors title them as if it will give you Vim mastery, but instead it only offers the basics.

Mastering Vim means going beyond vanilla movements and learning all of Vim's nasty warts to replace good GUI features. It means learning the wonky, dead Vimscript language. It means knowing how to use the arcane arglist. It means knowing how to go into insert-normal mode, and when to use the expression register. It means knowing everything about very magic search, and why default search is poorly designed. These are all randomly chosen examples, because mastering Vim involves mentally juggling a very large playbook of oddball features to complete editing tasks.

The main resources to help you master Vim are the book "Practical Vim" by Drew Neil, and if you're ever in the unfortunate position of needing to write or edit a Vim plugin, "Learn Vimscript the Hard Way" is invaluable http://learnvimscriptthehardway.stevelosh.com/