Correct me if I’m wrong but the claim is that the handicap game results on OGS approximate a 50% winrate for either side, better than EGF ranks do. (2020 Rating and rank tweaks and analysis).
I personally find this very hard to make sense of, seeing how a player on OGS can be 1kyu one week and 6kyu the next week. This could mean up to 10 stones swing in a handi game between the same players.