It was primarily a safeguard put there to avoid having his site / the charts used for erroneous balance arguments from people who don’t know what they are talking about.
He’s absolutely right that it measures metagame balance around the top of the skill ladder, and not actual balance.
The metagame is constantly in flux which obviously makes it hard to measure balance, and the sample includes the absolute highest skill players which means the outcomes of games are decided by skill and not by balance in 99.99% of scenarios, which also makes it extremely difficult to measure balance.
You’re basically trying to measure how a drop of water raises the levels of the oceans during a hurricane.