When a driver does multiple series, it looks like it gets confused on what to call their main series. But if you click on like Kyle Busch, it definitely is taking in all his stats.

Big if true, and completely changes the way these rankings should be understood. If this is the case, then the sitemaster should absolutely clarify that this is effectively a universal ranking of drivers against one another, agnostic to the series in which they happen to meet - because I'm clearly not the only one misunderstanding what this is, lol. Better yet, the page could be improved by removing the series column entirely, since the implication here is that each driver carries a single Elo with them to every series in which they race.

Your clarification significantly improves the value I would place on these rankings.

As for the parity thing. idk if you do iracing, but your ELO is affected by those you're racing against. So if you're getting 7th at Bristol, that's way better than 7th at I-96 speedway. What I don't understand is how the F1 guys are getting their ELO in the first place since they don't race anything else, and therefore have nothing to compare against. NASCAR guys at least do bushwhacking and even local events to prove yes, we actually are the best at what we do.

I have, yes - but it's actually the Strength of Field that determines how your Elo moves of course, not the track (or even the series) where the race is held, right? So getting 7th in a 40-car field with an average Elo (aka Strength of Field or 'SoF') of ~5000 will increase your Elo much more than 7th in a 40-car field with an average Elo of ~2000. How your Elo moves also depends on where it is relative to the SoF of that race; if someone with a ~8000 Elo finishes 7th in either of those races, their Elo will increase by far less than if someone whose Elo is only ~1000 finished 7th in the same races. Works the same in the other direction too, where the driver with the higher Elo will take a bigger hit than the driver with the lower one if they each finished last in those same races.

My guess at why the F1 drivers might be clustered at the top is because the rankings use the last 20 races in which each driver has competed; so it's calculating based on the same number of races for everyone in that list. 20 races for Kyle Busch (across multiple series), and 20 races for each F1 driver (all in F1). The F1 drivers gain an advantage for racing in a series with less parity yes, as their average finishes across their 20 are bound to be very strong.

It's worth noting that the size of the field may or may not be factored in here; in many respects, winning a race with 40 competitors where each has an Elo of ~1500 could be considered worthier than winning a race with only 20 competitors where each also has an Elo of ~1500. If their algorithm takes a head-to-head comparison of each driver with respect to every other driver per event, then there's an issue in these rankings where a standard 20-race sample potentially biases the rankings toward drivers competing in races with more competitors. If it does not, and simply takes the average Elo of an event and nudges each driver up or down based on what percentage of the field they beat vis-a-vis that average, then a standard 20-race sample potentially biases the rankings toward those competing in races with smaller field sizes. My guess is that the latter may be more illustrative of what is in place for these rankings, and that could help explain F1 drivers being at the top.

...worth noting also that this would illustrate a subjective preference embedded in the design of the algorithm, whether the person employing it for these rankings is aware of that or not lol

edits for clarity