...I think there’s one misunderstanding about fargoratings that contributes to the belief that table size should affect it. People think your fargorating is an absolute measure of ability rather than a rating relative to opponents.
Statistically everyone should run out more in 9 ball (break rules being equal).
The above are indeed the two things that the "but it allows data from three plus different table sizes" and "but it allows data from three different pool games" people fail to fully appreciate and comprehend.
As BRussell pointed out FargoRate is not really a measurement of your pool skills (although it can be used to make good inferences about your pool skills), certainly not any kind of direct or absolute measurement. It is a measurement of how often you win or lose against other people, knowing and keeping in mind how often your opponents also win and lose against other people. Put another way, it is not trying to measure how many racks you can run, how straight you shoot, how tight of position you can play, how many spot shots you can make, or anything along those lines. It measures the most important thing, and really the only important thing when it comes down to it, which is how often you win or lose, against who, and by how much. FargoRate simply compares how often you win, who you can beat, and by how much against the same for everybody else and then assigns you a number in the pecking order such that those you would end up winning twice as many games as they do over time are going to be ranked exactly 100 points lower than you, and those that you would only win half as many games as over time are ranked exactly 100 points higher than you.
As Welder84 points out, people also tend to forget that whatever is true for them about the table/game etc is also true for your opponent as well but they always seem to forget that that part and so they fail to understand that proportionally things stay about the same between them and their opponent relative to each other regardless of the table size or whether the game is 8, 9, or 10 ball.
But I play way better on a bar box. Yup, and so does your opponent.
But a tight 9 footer is so much tougher than a loose Valley bar box. True enough, but that isn't only true for you, that also holds just as true for your opponent too.
But I can run 4 packs on a bar box and can only run 2 packs on a 9 footer. And your opponent can run 6 packs on a bar box and only 3 packs on a 9 footer.
But I run way more racks of 8 ball on a 9 ft table than I do racks of 10 ball. Yeah, and the same is true for your opponent. No, but I mean waaaaay more, I don't think you understand. And your opponent is running waaaaaaay more too, it is you that is not understanding.
And then the one final thing they need to understand is this, even if they never can grasp any of the above. Whether it seems intuitive to them or not, and whether it is what they would have thought or not, and whether they can grasp it or not, and whether it makes any sense whatsoever to them or not, there is now over 19 million games of data showing that you win at about the same rate against the same people regardless of whether you are playing 8, 9, or 10 ball, and regardless of whether it is a 7, 8, or 9 foot table.
You aren't alone in your incorrect belief, almost all of the rest of us expected there to be some difference too because on the surface it seems intuitive. But which do you really think is more accurate, your guess about what you would have expected to be the case, or what 19 million games of data actually very clearly shows? Which do you think is more accurate, what you thought you had noticed over time in your experience when you weren't even keeping careful track, or what 19 million games of data actually very clearly shows after it has kept very careful track? With 19 million games of data behind it the times of having to guess, or speculate, or for it being reasonable to still have some doubts are now long gone. With 19 million games of data this is a settled question, a long settled one. The game and table size (within the confines of those listed above) don't make very much difference in your win rate and 19 million games of data prove it regardless of what you thought you saw, regardless of what you would have guessed, and regardless of how intuitive that may seem to you.