Actually it has more to do with how that power is transfered. A smaller diameter bullet if it is designed better can be more effective than a large solid slug. Most centerfires use fairly light bullets yet they will knock a deer down in its tracks. This is because they have way more velocity and better bullet designs.

Most of the newer modern sabots use a XTP based bullet in 50 caliber that has a better BC and can deliver more hydrostatic shock than a regular large diameter slug can.

Paul