Well, we are bigger than we used to be, generally
and I know I am, personally.
A century ago, 250lb men were uncommon, heights above 6 ft were uncommon. Today, they are a lot closer to being common, especially in the US. Diet, vitamins, medical care, all have been improving the physical condition of our species, so, it is quite possible that overall, in the US, we are more difficult to stop than our forefathers.
However, since we never meet the general overall in a defense situation, the point is moot. What we meet is an individual, as likely to be under average as over average.
Each encounter is an individual, and while generalities apply, they cannot be depended on as relative to any individual situation. Except for one. Shot placement over rides all consideration of caliber. Period.
A flesh wound with a .44 (or a 12ga) is not as effective (physically) as a CNS hit with a small caliber.
The military's criteria for a "proper" caliber are not the same as what a private citizen should use. Recent trends (in the last half century) to small caliber arms is based more on the capability to carry more ammo, and thus increase the hit probability. The Military mindset is about stopping the enemy from being able to continue combat. Killing them does this, but so does sufficient wounding. The ability of the round to protect the shooter in a self defense situation is not the paramount criteria. The mission is.
After the failure to perform satisfactorily during the Moro campaign led to doubts about the "small bore" .38 Colt, ultimately the creation and adoption of the .45 ACP, a round duplicating the ballisitics of a round still trusted by the military. The US found something that worked acceptably, and kept is for over 70 years.
Virtually everthing works when it goes in the right place. And all the different calibers and pistol designs are attempts to find a perfect balance between people's ability to use the gun effectively and their needs for portability/concealability.
My personal experience is in my sig line.