I just don't see it? I spent a good 6 months only using vim to see if I could get it to stick. Then I took a year break. After the break I forgot nearly every shortcut I was using minus a select few. I never got to the point of even matching my efficiency in other editors, let alone surpassing them.
6 months alone is already more than what I would consider worth in regards to time spent learning a tool for the little gain I see it bringing over just using intuitive, albeit less efficient, alternatives.
I do think 6 months should be enough to see some benefit in your workflow (like ci" to delete everything between "" and go into insert mode or Ctrl-O to go back to the last place you jumped from).
But I guess it depends on how you practiced, and if you look at those 6 months I'm sure you'll see that the time spent on actually learning Vim (struggling to learn these efficient editing patterns) was much less than you'd think.
With a tool like Vim I don't think it's enough to just use it, but we need to put conscious effort into it to learn it properly.
Also, although historically that hasn't really been part of the Vim ethos (compared to Emacs at least), you're expected to mold your editor over time to suit your needs exactly.
A tool that can last a lifetime and be used for any programming language at that.
It's just a trade-off between optimizing for the short-term or the long-term.