It’s not just the ability to grow own roots that becomes important, it’s the characteristics of the soils of your potential market.
In my garden, in the eastern US, the own root ramblers from the early North American hybridizers do well. They also worked in acidic soils.
This is in contrast to the puny performance of that most popular of own root roses, Dr. Huey, which sputteringly survives in this part of the country, but does (according to books about rootstock) much better in slightly alkalin conditions.
Alkalinity (and lack of same) as well as micronutrients matter.