that... isn't very useful, since you need premium to do many puzzles.
Puzzle percentile
I have a premium account currently, and during the periods of time when I was doing tactics training here, I did exactly the same number of exercises daily which I used to do when I didn't have a premium account (5/day). After around 250-350 puzzles, you get to know your real rating. That equals to around 50-70 days of doing tactics.
It's not that much, and many people have done way more than that, premium or not.
Why is there no puzzle percentile in the 'stats' section?
For example, 98.5% meaning that you're rated higher than 98.5% of rated players.
I think it could be added, just as it is for Bullet/Blitz/Rapid.