Yes, I will reword my statement to say “a factor” and others do agree. @no.stirrups is a saddle fitter, so I hoped she would mention some other factors she considers. I did check her blog, but it only mentions fit for the horse. In my experience, deepness of the seat makes a difference too. I’m petite, but have ridden in a 17.5 saddle because the seat was very deep, giving me less area to sit.
If you look at photos of riders of all sizes, you will see different flap lengths and placements of knee rolls to accommodate leg length. For example, look at Edward Gal. He has a very long leg and his saddle is designed to fit the leg. It’s not uncommon though, to see a rider whose leg goes over the top of the knee roll. To me, that means the saddle is too small or the knee roll is in the wrong place.
Not everyone buys a custom saddle designed to perfectly fit their anatomy. It can be a challenge to find one that is a good fit for horse and rider. How often do we hear a rider say the horse loves the saddle and I hate it or vice versa?