Too many cop videos tell me that 9mm is far from optimal.
How do you define "optimal"? Optimal to me is one round of any caliber stopping a fight. That means one well placed round. It doesn't matter what caliber you use if you miss or don't hit an attacker in a vital spot to stop the fight. Optimal could easily be 12 gauge buckshot and nothing less will do. I just don't think that's very practical. 9mm is quite practical and quite sufficient for self defense.