Most FFLs seem to recommend a 9mm for men so the data starts out skewed. Many 9s are lightweight making a 9 a popular CC weapon. All in all, the 9mm is a very common caliber. The 9mm using FMJ has killed too many people to say it "isn't lethal." As they shoot at moving targets who know they are being shot at. The military expends a lot of ammunition. As gang bangers know first hit usually wins, there are a lot of shots fired gang banger shootings. In this Conflict, too many observed head shots prompted investigations. The answer was the enemy was sticking his head up too many times and pop. Some of these shots were at ranges were the 5.56 is well known to be "ineffective." My 2¢ is ineffective becomes effective if accurate and effective is ineffective without accuracy. As I was an active shooter and reader back in the day, Ayoob's articles sold magazines; so did Jack O''Connor's and Elmer Keith's. They were excellent knowledgeable writers and America had a lot of shooters so the timing was perfect. Men who in 20 years of hunting harvested a deer a year in thick east coast forests bought a rifle because it was "X" inches flatter at 200 yards. Same as the emperor's new clothes, no one dared say "the only place you will ever shoot 200 yards is at the range.. Ayoob, Keith and O'Connor are some of the greats at shooting and stirring the pot.. Comparing their words with a Grunt's they all work if you do your job was and is a losing proposition.. I am no disagreeing with Ayoob, O'Connor or Keith; as Bruce would say I'm "just say'in."
it has NEVER been about Caliber, Load, or Projectile...... It has ALWAYS been about SHOT Placement..... The rest is ALL, semantics.... ...... YMMV....
Neighbor and acquaintance of mine was shot twice in the head, once in the upper abdomen and once in the arse as he fell last September with a 9mm. He still managed to return fire and has since made a full recovery. Maybe luck, I dunno. But I'll never trust a 9mm to do the job again. Of course any gun you will carry is still better than the one you leave at home so to each their own.
The only SURE caliber is supersonic phone pole and even then it must be well aimed as most of us could only carry one round.
There is a saying; on any given day it is better to be lucky than good. Where he beat the odds was first hit(s) usually wins. It doesn't matter what some "internet" author/authority said, if you don't trust it, don't use it. Although there are exceptions to every rule; in general my experience was if the operator does their job, the firearm will do theirs.