I don't think there is a conclusive direct correlation between head shapes and bite power. I recently got into bitework and dogsports and these GSD, Malinois and xMalinois that have more of a long and "skinny" head compared to bulldogs can bite super hard. Depending on the lines, many of these dogs also have a full and pushing bite. Whereas in bulldogs what I notice is that the ones with a real finish have a full and pushing bite. Many of em are perfectly fine having a half grip and work their holds.