I’m not sure why 60 vs 40 is slightly better than random chance. A person using this system has a 50% higher success rate than those not using it. I wouldnt call this a slight better result.
You can see the plots if you prefer, or think of it this way: out of a total of 100 trials, one team gets 40 and the other gets 60 = 40 + 40 * 50%
If you want to think of a 75% win rate as a more extreme example: you could say 25% above random or you could say one team wins 3 times as many cases as the other. Both are equivalent but I think that the second way conveys the strength of the difference much better.
The results in this work are statistically significant and substantial.
