Well, it does work better for a left hander. I am lefthanded, and I have been shooting singleactions for close to 40 years. I have never seen a righthander that can load a singleaction as fast as a skilled lefthander. However, there very well maybe some, with cowboy action shooting as popular as it is.
But a lefty, can hold the single action in his shooting hand without every really changing the grip. He can index the cilinder with his index finger, while ejecting shells with his right index finger. Then without changing grip, he can thumb shells into the cylinder ports while indexing the cylinder with his index finger of the lefthand, snap the loading gate shut, and he is ready to go. His shooing hand (left in this case) never had to change it grip, during the entire episode.
I can load a singleaction this way, almost as fast as the vast majority of people shooting doubleaction guns, if they do not have speedloaders, and have to load with loose bullets, same as me.
Sometimes, I think Sam Colt must have been left handed. Plus think about this. A lefty with a strong side holster, usually would have had cartridge loops on the right side, which would be more accessible to his right hand, while he still held the gun in his shooting grip, where a righty strong side, would probably have his cartridges on the left side of the belt. Once again it's all backwards, for the righty. Something to think about anyway.