Why does the graph say one size is massively winning when up by only 1 point. Isn’t this formula need work?
Because if you are a superhuman AI, winning by 1 point can be massively winning. That’s the important thing to note about AI winrates, they are not targeted at YOU the human weakling 5 kyu or whatever. So if you are assuming an AI winrate of 90% means you have a 90% chance to win the game you have misunderstood it. This is one reason why using score rather than winrate is generally much better.
Win rates are generally not very useful, humans are not perfect and have emotions so we will therefore throw games when they are massively winning, even at higher levels sometimes. I have had lots of games where me or my opponent were +30 but still managed to lose because of playing tricky moves and not giving up.