Is Pantheon fixed?

Could someone explain how a "placebo" on buff W could have such a big increase in his win rate?

14.18 (pre item nerfs) https://lolalytics.com/lol/pantheon/build/?patch=14.18

14.19 (item nerf patch) https://lolalytics.com/lol/pantheon/build/?patch=14.19

14.20 (current patch after buff) https://lolalytics.com/lol/pantheon/build/

Post buff win rates have climbed to be very close to 14.18.

If such a small buff on one ability increases his win rate so much, seems like the other buffs suggested in other threads (like all the mana suggestions) would overpower him to be nerfed. Is he in a good spot and do people actually feel his buffs? If people can't feel his buffs, it's a concern that pantheon's actual strength might be weakly correlated with people's perception.