First, a consistent winrate of 53% COMBINED WITH (this is the part you keep ignoring) the high pickrate demonstrates that the champion is very popular and popularity implies that she is played often by casual players. If casual players are having great success with a champion not even having bothered to master her, then that suggests she is very easy to play and/or her power is a bit too high when even a casual player can win well above the statistical mean.
As to your point about a "60% win rate", I don't recall a champion in League history EVER having a 60% win rate outside of the first week of the juggernaut update when Skarner was briefly at 65%... he was hotfixed and that was the end of that. I've seen a couple briefly get to 59%. So, I don't think that's a great example.
Ahri has safety, sustain, true damage and, most importantly, mobility. In League, very few champions have all of the items Ahri brings to the table, most champions have a tradeoff somewhere, that being if you have sustain, you usually have lower base stats, or if you have good poke you are usually immobile---like Vel'koz for example. Vel is really the poster-child of how a champion should be... lots of poke, all skill shots, high damage if your combo lands but his tradeoff is that he is very easy to gank or abused by mobile champions. Ahri doesn't have these weaknesses.
You might say, "yeah, but you can blow her up with CC" --- that can be said for any champion. Ahri doesn't really have a weakness other than her early mana costs, but even that's only a brief window of the first 10 minutes of the game or so.
I'm not saying she's "omg overpowered gut this bitch!" but I do feel that a champion that performs at such a high level and with such a huge pick rate must, at some point, be examined for nerfs---even if they are subtle.
I think removing her move-speed boost on Q would be adequate, her win rate would drop slightly and the subsequent pick rate would drop.
I don't usually lose to an Ahri. I will say this, if I pick a newer champ midlane, one that I haven't played frequently and I'm against even a mediocre Ahri... I hate it, I'd rather play against Yasuo 100 times out of 100 than Ahri if I'm not on one of my mains. I'm not even great at this game and even I can carry on Ahri most of the time when I decide to play her.