The cowboy shooters have been cocking the SA with the off hand for some time now, and their speed is impressive and shows the potential of the technique.
Umm...yeah, it's fast. But only with mouse-phart loads.
Sigh.
OK, first problem is that to get that fast, you have to drop the off-hand thumb back behind the gun's upper grip area (across the "web" of the strong side hand) at the end of the cocking stroke, just before firing.
Try shooting BIG power like that sometime. With any gun...stout 45LC or 44Spl will hurt like hell, edgy full-house 357 will damn near rip your thumb off. (NOTE: for God's sake don't ever try that with an auto - the slide is liable to slice your off-side thumb.)
Second problem is, do that too much and you won't be able to shoot one-handed worth a damn. And that skill is absolutely vital - with any gun. Your off-hand might be tied up doing something else, like keeping your kid or wife behind you, or grappling with a goblin, or just shot up.
Off-hand-cocking with two hands is something that developed in SASS/CAS because of low-recoil loads (even in 45LC) and the fact that most SAs have hammers that are too long - cloned off of post-WW2 Colts. The hammer reach of a pre-war (1st gen) Colt SAA is identical to my *modified* Ruger.
My gun may not look period-correct, and in most ways it certainly isn't, but at least in terms of hammer cocking feel it's more correct than a brand new Colt SAA.