There’s been a couple mentions already, but not much attention. Eventing has a pretty good solution to this. At each level the divisions are Horse, Rider, and Open. Horse and Rider divisions are restricted to the respective member of the team not having completed more than 2 levels above where they’re entering. (It used to be more than one level above, which I think was better.)
So:
Horse division = any rider on a horse that hasn’t competed higher.
Rider division = any horse, with a rider who hasn’t competed higher.
Open = any horse and any rider.
If entries warrant, the Rider division may be further broken down as Junior and Senior by rider age.
Not uncommon for the Training Rider division to include a mix of true ammys, working students, low-level local instructors, and occasionally a professional from another sport.
It sounds like the BLM divisions were patterned along this model. Here’s hoping it catches on. It’s the closest thing to a level playing field I’ve seen.