Drawing a gun from a sash while standing upright is a problem. Its much less so when sitting in a chair, leaning forward, when you are playing poker. The front of your coat tends to fall away from the body, giving better access to the sash and guns. The guns "slumping" actually makes them easier to grab- cross draw.
Yes, Hickok is shown wearing holsters- but virtually 100% of photographs HAD to be posed in those days. You are seeing prop guns, and rarely the subjects own guns. The holstered gun was much easier to show.
Hickok was Not a big man. He had small hands, which favored the small grip of the 1851 Colt model revolver. I serious doubt that he used any 1858 Colt or Remington .44 cal. revolver as it was too heavy for him, and the grips were too big for his hands. Too much mis-information about Hickok dates to the TV show with Guy Madison acting the part of Hickok. Madison was a tall, good looking Hollywood actor who played the part. Anything he did with revolvers were things taught to him by Stunt Coordinators.
The nice thing about carry the light 1851 .36 colt revolvers in a high sash is that the gun is carried in about the exact same location as a modern shoulder holster positions the gun. If you are standing, you can cross your hands over your chest, and conceal the movement the hand closest to your jacket to reach the but of the gun under the other arm.
Once your hand is around the grip of the revolver, you are about 1/4 second from being able to draw and fire the gun at an assailant. You draw the second revolver as you move to cover after firing the first shot, to protect yourself from any other assailants who are waiting to catch you with your back turned to them. Going from a position where you appear to be an unarmed "victim", to a man now holding 2 guns, and already having shot the first assailant is a sure " Game-changer" for multiple assailants. The reason they hunt in packs is because they are all cowards, and they certainly don't want to be shot.
Enough about gun-fighting tactics, and mental preparedness. I only mention it because there was a real Method to his choice of wearing a colorful sash at the gaming tables, which is not well understood by even " gun Experts", these days.