Yes, it started as ELO, with 1 rank = 1 stone, which I think acts as a pretty good basic system for rating generally. In my opinion Glicko2 is just a good evolution of the ELO system, which suffers from certain simplicities (particularly ignoring rapidly improving players, or at least players not playing very much therefore changing nominal strength quite quickly over the course of “games played”).
Ratings and ranks are something I can sort of rant and rave about for a long time as I have fairly strong opinions which I’ll try to curb somewhat, but I suspect there is no perfect system, and what is adopted I think depends on what you’re trying to achieve. It is a lot harder in Go where there is a lot of intrinsic psychological baggage attached to rank.
Professional dan titles make a lot of sense, where they are earned and not lost, and earned based on specific achievement milestones. Outside of that, the purpose of any form of rank and rating system is to provide sensible matches, an understanding of “approximate” strength, and relatively uniquely to Go a benchmark for appropriate handicapping. Despite this, people have great desire to be SDK, or reach the coveted dan ranks, despite the fact that amateur dan ranks are so variable.
Essentially all of the main numerically based rating systems create a bell distribution of players, and the more players you have, the further towards each end of an infinite scale the outlying players go as the curve increases in scale. Furthermore, if there is a steady improvement in overall playing strength of a playerbase without some form of controlling factor, you get rank drift. A crude example of this would be if 400 people are all 6k and only play each other yet improve at the same speed, once they improve by 6 stones, they will still be 6k as the only place to grab rating points from is each other. despite having all become considerably stronger. There was a big discussion when I was a British Go Council member on how to handle this (the EGF slowly injected points into the system by a small amount for each submitted game, I don’t know if this is the case still).
As a result, all you can really aim for with a rating system is “anything that achieves the following”:
- People who don’t play that often don’t end up finding their rating incorrectly assessing their comparative strength for too many games before it corrects itself (Glicko2 is actually pretty good at this)
- The grades that are assigned to the rating levels offer more or less correct handicap (interestingly, the faster the time control, the more of a handicap is generally required, so this may need different weighting for different game speeds - again, OGS does this well, and that’s a post merge change with the Nova crew!)
… and that’s pretty much it. Whether a specific place tells me I’m 13 kyu or 6 dan doesn’t overly bother me, what’s important is that it’s internally consistent rather than the specific rank it tells me I am. I also think this is why it’s so important that if someone tells you their strength, they also tell you where that strength was given - KGS 1 dan, OGS 12 kyu etc, is of much more value than the rank by itself.
I think the rating system for OGS seems pretty good, and serves it’s purpose well. I do wonder if it seems a bit top heavy, as there seem to be a large number of very strong dans and not very many players around the 20 kyu mark, but maybe that’s because I’ve been hanging with the wrong crowd. Any form of rank to rating adjustment would fix it if that’s the case, but it’s not particularly critical to change anyway for the reasons I’ve mentioned above.