I don't think anyone is going to argue that round for round, .40 is more powerful in standard loadings than either 9mm or .45.  Math works that way and it's just a fact.  10mm of course is superior in every respect to all of the above.  The question becomes is it enough of a difference to make a difference.  I say it is in some cases.

We have about 3 shootings a year in our county.  Over the last 10 years I've noted that those suspects shot with 9mm required more shots to stop them than those shot with .40.  Not many more, maybe one or two, but more.  I know there are many factors involved but it has been pretty consistent over a long time.  We however shoot many many deer at the side of the road.  Average about 3 shots to dispatch with 9mm vs usually 1 shot with .40 or .45. 10mm also, but I only know of one deer with 10mm and it was a 1 shot DRT.

Now, that being said, those shooting 9mm tend to shoot tighter groups than those shooting real pistols.  I'm not talking laser vs shotgun, but even in myself It is noticeable that my 9mm groups are smaller with like pistols.  I have 9mm and .40 barrels for my Sigs and my 9mm groups are consistently about 1/3rd smaller.  This seems consistent at the range when instructing other deputies.  Those with 9s tend to shoot smaller groups at qualification.  I would however note that those groups are probably not smaller enough to make a difference in a real fight.

Where the 9mm does however shine is in capacity.  Again, using my Sig p226 as an example, I have 12rd .40 mags x3+1.  In 9mm I have 18rd x3 +1.  That gives me the equivalent of a 4th mag on my duty belt.  While the ammo is less powerful, I have more of it in a package that allows me to shoot tighter groups.  This may be less important on road patrol where a suspect is more likely to be isolated and not tightly packed into a crowd.  I am however assigned to a school district.  An active threat is highly likely to be in a crowd and I have an extremely low probability of getting to my cruiser to retrieve my long gun in an emergency.

This thread is timely as I was making an observation yesterday after shooting three of my pistols back to back.  I made the mistake of shooting best mm first.

G40 mos, very satisfying, Hammer of the gods

Sig 229, sorta good, maybe not thor's hammer but at least a lightning bolt or something.

Sig 226, meh, felt sort of like Captain America before the bio engineering.