He isn't in the most banned because he isn't in the most played. He is mechanically higher than some champs and some people just don't have high mechanics. When he is played by someone who knows how to play him it is pretty obvious how broken he still is, he just isn't brought out enough to warrant banning when the easy mode champs are played by everyone.
It takes very little skill to play Jarvan, or Fizz, Or Rek'Sai for example so more people play them because they are easier to learn and get going with much less practice as you don't have an extra skill on every button like with Lee for example.
So while your example probably sounded good to you it isn't actually a valid one considering the above points.
If you were to play Lee Sin and do bad, you might not play him again, same with 10 people, and the opposite would go towards you playing Jarvan, he is much easier so you will have an easier time and higher chance of succeeding, same with the 10 people. Chances are you and those people will play Jarvan a second and third etc time to where a pattern forms, where you see the one...maybe two Lee Sin games, you compare the amount of games between the two and it is pretty obvious at that point which you'd ban.