The reverse cavalry draw or "praire twist" is not dangerous.
I tried to convince a group of this, and the semi-auto guys nearly castrated me! Well, yeah......I guess with a semi-auto it wouldn't be a good way to carry, but with a revolver it is just fine.
Again, look at 1800 period photos and see how many "cross draw" holsters you come up with.
A century is a long time, and the 19th century covers a huge part of revolver and holster development. I have found that cross draw and twist draw seemed to predominate until some time after the Civil War. Period photos from the 1880s on seem to favor the standard draw. It's all evolutionary, and shorter barrels became more popular with time.