If my only concern was people, I would rock a 9mm and never look back.
That said, people are not my only concern. They are not the only concern of a great many Law Officers throughout the country once you get away from the urban areas.
Typical medium to small animals, a 9mm works fine, and that includes thin skinned critters like cats (I am talking about mountain lions and bobcats not domestic kitties) and coyotes.
When you get into larger animals is where things get different.
This is where people have entrenched thinking. When they think "large animal defense" they automatically think "Bears". The fact is that the odds of going up against a bear are rather low as a lawman, or as a citizen.
You are FAR more likely to be injured or killed by a horse or cow than a bear by a substantial margin. I have put down more injured cattle than I can recall.
There are not many places in this country that do not have cattle and horses.
Cattle trucks overturn on the interstate/highway.
Trucks hauling both cattle and horse trailers are involved in vehicle accidents every single day on county roads.
Animals get frightened during storms and run through barbed wire fences, injuring themselves.
They constantly wander onto roadways, getting struck by vehicles, becoming injured and still mobile.
Huge parts of the west have land that is legally called "Open Range" where livestock have the right of way.
Sometimes they just get sick,
etc, etc.
The only time I ever actually used my straight stick on a live object was not on a person. It was on an injured cow from an overturned cattle truck. That cow had flipped one guy off his 4 wheeler, and had two people pretty much corralled in the back of their pickup bed, and had dented the side of the truck a couple times as the guys were waving the cow away from the interstate. I was running away from and smacking that mad SOB hard as I could (imagine a rodeo clown keeping in tight behind the shoulder of a bull trying to gore him and you get the picture). My ASP looked like a banana.
The supervisor (who was not there) had initially refused to let me shoot the animals, even though we had an interstate with 2 lane traffic (each direction) running full speed .
Eventually a crash happened with one of the cows that I could not prevent due to this order. I remember watching it like it happened in slow motion and there was not a thing I could do to prevent it. Everyone was doing their best to round up the few cattle that were not aggressive, and one slipped through and trotted up onto the hardball.
The man in the passenger car died as I spoke to him. An autopsy later revealed a detached aorta. After that I went to putting down the couple of remaining cattle that were loose with my .45. That caused some huge problems and internal fighting as I had chain of command both for and against my decision to disobey orders.. anyways..
My personal experience is that for large animals, a large heavy bullet gives you better penetration against heavy bone and tissue. Especially when your shots may be at a less than ideal angle.
When your average to large Angus bull weighs in at about 1 ton and a heifer at 1/2 that roughly, and you need to put one down DRT, I would rather have a larger caliber handgun than a smaller one.
You can kill the stupid things with a .22 to the ear canal, but there is a big difference between an animal in a loading chute, and a hell bent one on the loose in a town full of people who don't know any better than to get the hell away from it.
Just my experience.