Try hunting a 400 lb boar with a 9-mm +P+ and see how fast you kill it. You will likely have to empty the magazine and end up getting mauled. The 10-mm does it with one or two shots. Weight makes a big difference as it is constrained by F=ma which never fails to prove itself true. Bigger bullets like any other projectiles do much greater damage to tissue or hardened structures.
The discussion was about people stopping power, not bear stopping power. Few people have to ever fear 4 legged creatures.......it is the 2 legged variety which is dangerous.