Forgive me if this has already been discussed and dismissed…
It would seem more logical to categorize based on FTP in watts rather than w/kg. Many of the races are held on predominantly flat terrain. While w/kg is going to determine speed on climbs, absolute wattage is what is going to determine speed on flatter terrain. With the current categorization based on w/kg, lighter riders are penalized.
In real world cycling, if a 65 kg rider has an FTP of 3.0 that would be 195 watts, vs. a 75 kg rider of 225. On the flat, the 75 kg rider will be faster and have an easier time remaining in the draft compared to the 65 kg rider. That seems to be how the Zwift algorithm works of the flat, as well. Conversely, on a hill, they will be equivalent where the draft is going to be less effective anyway.
Ideally, an automatic categorization would be make based not he Zwift estimate of FTP which it already has data for. W/kg would still be available to identify flyers. It would just be the initial categorization.