"Ahri is more appealing than Urgot for most players, so we expct Ahri to be more popular than Urgot"
Ahri is more appealing because she is stronger. If you want to test this out nerf ahri to urgots winrate and buff urgot to ahris winrate. Then lets see which is more appealing.
Also, people will always play stronger champions because they want to win. Not saying everyone will, but a lot of people will. That is why when a champion is overbuffed you will see a spike in their winrate and popularity. Take lux for an example, before they buffed her she had a ~50% winrate and 5%-8% popularity. After they buffed her she spiked to 15% popularity and 53% winrate. Basically, because she is stronger more people are playing her. Take skarner as another example. When that champion was buffed and his winrate spiked to 60%, people who never played that champion before played him if he wasn't banned.


are good examples of the former.
are good examples of the latter.