Sammy Sousa may have used a corked bat but so what. The man has power, speed, control and accuracy that majes him a legendary hitter.
I am unsure of the in’s and outs of legal bats but a bat has a “sweet spot” where you know you knocked the ball out of the field when you feel and hear the sound.
If you want to improve you have to practice and practice knowing how. Bat Speed and Power Hitting tells you some of what Sammy Sousa already knows. If he knew it was corked shame on him he did not need it.