This thread shows a severe lack of knowledge and understanding of terminal ballistics.
Bullets incapacitate by destroying soft tissues (blood vessels and organs) which leads to massive loss of blood lowering blood pressure to the point the individual can no longer function or by destroying the Central Nervous System (C7 or above). To do this a bullets primary job is penetration as without sufficient penetration none of the above will be accomplished.
With penetration being equal diameter becomes important in that a larger diameter bullet destroys more than does a smaller diameter bullet. The advent of bullet designs that offer reliable/consistent expansion while maintaining adequate penetration allow a bullet to effectively increase the amount of tissue it's able to destroy, increasing it's effectiveness.
So while expansion with adequate penetration increases a bullets effectiveness, expansion that results in sacrificing adequate penetration decreases the bullets effectiveness. In the '80's the current thinking was all about expansion and energy dump to induce incapacitation and the hot JHP loads of the time reflected this. The Winchester 9mm 115gr silvertip fired by Agent Dove in the Miami shootout did exactly as it was designed to do yet failed to end the fight. The FBI shootout with Platt and Matix set in motion research into terminal ballistics that has changed how we look at tactics, advanced realistic training and lead to today's development of several excellent self defense ammunition choices.
Ammunition such as the Winchester silvertip and Federal hydrashock are older (inferior) tech and are not today's premium choices. Hornady's critical defense ammunition lacks adequate penetration due to a premise by Hornady that self defense for private citizens is somehow different than self defense for LEO's (critical duty). While there is no magic caliber or magic bullet there are good choices and poor choices, it behooves one to put aside urban myth, brand loyalties and preconceptions to research and educate ones self as to what it takes for a bullet to effectively do it's job.