I disagree.
I shoot guns like this from the Weaver, thumb-cocking with the strong hand, and if necessary adapting the gun's ergonomics to my hand size. Ruger has several hammers with different "reaches" available, that drop in or require minimal tweaking to install. They're less than $40 a pop. My New Vaquero sports a SuperBlackHawk hammer and if I had the larger XR3-RED grip frame ("Old Vaquero") I'd have dropped all the way to the Bisley hammer. (The Bisley hammer needs minor filing on the back edge to make it fit non-Bisley grip types, but it's very easy to do with home tools.)
My biggest gripe with the CAS/SASS sports is that they disallow these simple ergonomics tweaks. In the REAL "old west" many more gun types were available than are replicated today, so getting a proper fit to your hand was much easier. CAS/SASS has forced everybody to adapt to one gun type and as you say, most two-handed shooters are having to do this weird off-hand-cock...which in a real fight might get you killed if you're forced to revert to one-handed either due to extreme movement or injury.
CAS/SASS is literally forcing people to adopt techniques that should not be used outside of the "sport". Rather than preserving old skills, they preserve the cosmetic appearance of "authenticity" borrowed as much from "B Westerns" as reality.
And all this banning of cheap ergonomics mods happens while far more expensive *internal* mods are "OK". Like the Power Custom drop-in hammer/trigger sets at almost $200 a pop, or steel grip frames instead of aluminum, or line boring for God's sake. It's as if NASCAR teams could do whatever they wanted to the drivetrain, but were locked into a particular seat/steering wheel/pedals set and positioning for same.
It's absolutely insane.