champion.gg is not a reliable argument to say that a champion is a counter to another

Once I tried to explain on those forums that Vladimir is a counter to Yasuo, then someone presented the fact that Yasuo has a 52% winrate against Vlad at top lane. Then I explained that the possible reason for this is because Vlad is a more common champion to be used at top lane, while Yasuo is a less common. People that play Yasuo top generally have more experience with him than people who play Vladimir at top lane, while the reverse is true for the mid lane. In addition, top lane is a larger lane that favors all-ins more, something that Vlad is weak against and Yasuo is good at during the early game.

That said, Vladimir has a 56% winrate against Yasuo at mid lane, by the opposite reasons that I explained above.

But the main idea I want to say is that champion.gg is not a reliable source to say that a champion can be used to counter another, because champion.gg generally just takes winrate into account, without taking into account whether a champion's kit can actually be used to counter another champion's kit.

Why I am saying that? Because I just got to Fizz's page at champion.gg and there it says that Karthus counters Fizz and that he has a 57% winrate against Fizz. When I saw that, I realized that this site just can't be used to justify counters, because there is no way that an experienced Fizz could lose a lane matchup against even the most experienced Karthus. The former's kit is just a complete hard counter to the latter's kit, there is no way that Fizz can die to Karthus and he can even towerdive Karthus as many times that he wants unless Karthus plays extremely safely, and he will probably lose a bit of CS.

Then, how to explain Karthus having a high winrate against Fizz? Well, Karthus is a champion that is much less commonly seen at games, compared to Fizz. Generally players that play Karthus have an higher chance of being experienced with Karthus than Fizz players being experienced with Fizz. A smart Karthus will do everything possible to deny Fizz: from taking Exhaust, to farming and playing safely. Karthus will actually outscale Fizz at late game, and will be able to do much more for his team, and have a higher chance of winning teamfights. All those factors may explain why Karthus wins against Fizz more than he loses. But that does not make Karthus a counter to Fizz. It just means that Fizz is not among the best counters to Karthus.

To be honest I've yet to found a site that can explain 100% of what a champion can do against another, because most of those matchups are skill based and there is rarely a champion that is a complete hard counter to another.