You don't seem to grasp the fact that cheating someone out of their money or a fair chance to win is worse than putting yourself at a disadvantage from an inflated ego. I really and truly couldn't care less if somebody said I was worse than I am. What difference does that make? When we play my score is my score.
Why worry so much about people bragging on themselves or saying they are better than they are? I've seen those people all of my life in every sport I ever played. None of that crap matters at all once the game starts.
Sandbagging is more in line with corking a bat, putting extra air pressure in the kicking ball, or using a banned substance. It's getting an illegal advantage to try to win and rob the honest players of a fair shot.