I don’t know about relative knockdown power of various handguns rounds, but I came to the conclusion working in an ER in DC during the 80’s, that you can’t kill a drug dealer with 9mm. They adsorb the stuff like a sponge, take a short holiday in the hospital and then get back to work.
While I'm not at all a strong proponent of the 9mm, bullet design has come a long way since the 80's. (Actually, I'll amend that comment - if a 9mm is the largest round a person can shoot well and train with regularly, then it's probably the very best round for them).
I'm not surprised at all about what you say, particularly if the 9mm was a FMJ which minimizes bullet deformation and consequently, tissue damage. One advantage of the .45 FMJ (apart from it's much higher sectional density) is that its lower velocity actually results in the projectile frequently stopping in the body which results in 100% of its kinetic energy being expended on the target.
The smaller caliber, higher velocity, 9mm FMJ will frequently penetrate the target completely, expending the majority of its kinetic energy in the wall or hillside behind the target. Newer projectile designs for the 9mm are far more effective in deforming and stopping in the target, as well as expanding to create larger wound channels.
Do you remember your one millionth customer?
Not to say there is a lot of shooting in DC........