The fact that you use win rate to judge a champion's viability only displays your own lack of knowledge.
If you use winrate, and nothing else, then yes. However, Riot uses winrate as a small indication of a champs current strength. BUT, you need to be careful. Some champs, like
, kits are so simple, and their game play is straightforward, that them having sub-50% win rates would indicate that they are doing poorly, while higher than 55% indicates that they are too strong. This is due to the consistency that they can play, what with the above reasons.
Other's, mainly the flashy champs like
, kits &/or gameplay are complicated enough that beginner's and the inexperienced **will ** fail. That, combined with a high playrate(for most), tanks their win rate considerably. If they had a high overall winrate, such as 52%, that would mean that even those who don't play them much would be able to win on them close to 52% of the time, which would indicate a problem as their power is supposed to be centered on their outplay potential, which is something one has to work at.
So winrate should not be the sole reason backing your arguments, but as a supporting fact it gives a great overview.
As for your complaints of Lee Sin, DrCyanide put it rather well.
That champion that fluctuates between 25% pick rate and 43% pick rate is at a high point right now. He'll drop down again, but as long as people keep thinking he's the solution to every problem and think he's fun he'll remain a high pick rate champion, despite nerfs.
Not to mention you said
nothing's being done to adress the issue
and
not necessarily nerfing or buffing
in the same sentence. How are they supposed to drive down Lee Sin's popularity, if said popularity isn't centered on him being overwhelmingly strong? And more importantly, why would they? It would be extra work, just to piss off their customers for no reason.
And one last thing,
Lee sin is at a 42% playrate
this has no backing, nor a citation(or even mention) of where you got it. Generally when you use statistics you are to say where you obtained them from, that way people know you didn't just make it up.
Op.gg says he has a ~26% pick rate, Lolking suggests that he has a 6.9% popularity. Both of these are far from your projected 42% play rate, so a citation would be nice.