Horses can certainly be ridden without stirrups. In fact stirrups weren't invented for over 4000 years after the domestication of the horse. The Roman Empire had no stirrups. The hardest part of riding without stirrups is mounting. It requires some mixture of strength, coordination, and a cooperative animal to mount from the ground without stirrups. Once you're mounted, staying mounted is not much more challenge than staying mounted with stirrups.
Yeah in deep water you either have to have somebody on the other side holding that gunwale down, or you have to pull yourself up on one end. Nobody boards that way from the shore, though. You just have it sitting in the water where it will barely touch bottom if you put all your weight in. Then you get in, and it's sitting on the bottom, balanced. Then you push off with a paddle or stick. The whole process is much easier than using a dock.
Yeah in deep water you either have to have somebody on the other side holding that gunwale down, or you have to pull yourself up on one end. Nobody boards that way from the shore, though. You just have it sitting in the water where it will barely touch bottom if you put all your weight in. Then you get in, and it's sitting on the bottom, balanced. Then you push off with a paddle or stick. The whole process is much easier than using a dock.