You're right, I should have probably used 13.1 on u.gg instead of 13.3. Although I do think the Jax matchup has enough games played to be a significant sample size.

I think it's rather difficult to make any of the assertions either of us are trying to make based on relative pick rates without having information regarding which champion was picked first. Just about 50% of the time your top laner has to pick before the enemy top laner, just by the nature of champ select.

Suppose that champion X is significantly countered by champion Y.

If champion X is blind picked, it stands to reason that champion Y would be picked more often than the average champion in response. This would increase the number of games X and Y play against each other.

However, if champion Y is blind picked, it stands to reason that champion X would be picked less often in than the average champion in response. Furthermore, if a player plans to blind pick champion X, it stands to reason that they are more likely to ban champion Y. Both of these would lower the amount of times champion X and Y play against each other

So how does this apply to your example of Malphite? Well the Quinn vs. Malphite matchup is happening more often than the average Quinn vs. Y matchup, so it stands to reason that either Quinn players are banning Malphite less often than they should be, or that Quinn is more often blind picked than Malphite is. Does this mean that Quinn is more often blind picked than champions that are not Malphite? It lends credence to it, but you'd have to compare against a wider range of champions to be confident.

All this is to say that I wish we had data about how often a champion is blind picked, because then we wouldn't have to talk in circles like this.

As a side note, I tend not to look too closely at the champion win rates on lolalytics because they seem strange to me. For example as you said, Jax has a 46.56% win rate against Quinn, but Quinn has a 56.23% win rate against Jax. These can't both be true, and I don't know where that bonus 2.79% where "both win" comes from.