Purposely going on the offense with any pistol is not real smart. While I have never been on offense or defense as a civilian I have carried and used one (many times) in the early 60's as soldier in South East Asia. I never pick a hand gun as my first weapon. When I did have to use one (carbine Jammed) The nine was enough to do the job as was the .45. Targets were Small folks with no body armor.
Why anyone would knowingly go into a fight with a pistol escapes me. It seems to me a question asked by some one who has never had to use a weapon. I don't mean to be disrespectful but the question is moot
HAHA
I dont think he was talking about killing people is South East Asia. I dont think he was talking about body armor or jammed Carbines. :-D Im not even sure he was talking about a war type situation.
Any-how as far as offensive and defensive goes, I think it is more based on the handgun.
*For example*
If you are on the Offensive you might be a SWAT team, or, a bank robber.
So, you might want a gun that has high cap mags., silencer, light or even laser. You are probably not worried about hiding it, so, bullet size would not matter, because gun size would not matter. You would want knock down power no matter what. Shot placement would only be in your favor if you were on a SWAT team and would get into trouble with wild shoots that were off target. The bank robber would not care as much about shot placement he would probably just want as many rounds as he could hold in one mag. . Also the person with the gun is probably the only one that uses it, and does not need to worrie about recoil. Because, he is used to or certified with the hand gun.
As far as defensive goes. When you are on the defensive end, you most of the time are surprised and have to act/think much faster, and you might not be the most fermiler one with the gun you are using. Like if in a break in, you are away but your wife is home. You would want somthing that is easy for her to use and operate, with a bullet that does not have much recoil. If you were to get mugged at an ATM, you would want something you could get out of your coat fast and get onto target with. So, with that being said you might want a smaller gun, meaning the rounds might be smaller as well.
I hope this helped, Like I said, I think it is more the gun not the bullet.
Goodluck.
Dave.