I can understand why mosley would feel that way. When you get hit with real accurate punches and shots that you dont see coming, they will hurt a lot more than it looks and he took a lot of those from floyd.
Canelo may be heavier handed and his punches might have more muster but that doesnt necessarily mean that his shots can cause more pain.
Floyd is a dangerous puncher due to his speed, timing, and punch placement.
Mosley fought both so he knows this.