Threads like this still make me sorta shake my head. Between 9mm, .40 S&W, and.45 ACP, they have all proven effective as defensive cartridges, and thus they remain popular. Though some speak of the eminent demise of the .40, I sincerely doubt it. Recoil varies between the calibers and can be mitigated or exaggerated depending on the weight and design of the firearm. Folks got to find what works effectively for themselves and stop criticizing others for their choices.
I have personally carried in all three calibers at one time or another. I do not find recoil of .40 S&W too much to handle, nor that of a .45 in smaller guns, but some folks do. I stopped carrying my .45 because I found the weight of my RO Compact a little more than I appreciated after a full day (partly because abdominal surgeries made the weight feel uncomfortable now), but the gun is excellent! It is accurate and dependable and I did not feel shorted by 6 round magazines. Carrying a spare mag gave me 13 with one in the pipe.
I changed to my XD Mod 2 sub-compact in .40 and got a slightly smaller firearm with a little less weight and 9 rounds per mag. This too is an excellent pistol, accurate and reliable and I still do travel with it.
A year ago I picked up a P365, and immediately loved it. It is by far the easiest to conceal on my skinny frame and the light weight makes it quite easy to carry all day long. The additional ammo is a plus with the slightly reduced power of the cartridge. It is as accurate as the first two and very comfortable to shoot with, and utterly reliable.
I have shot all sorts of light and small pistols in all three calibers. It is notable that it is not simply the weight or caliber that affects gun handling and perceived recoil, but the design/shape is significant as well. The caliber itself is often not the problem at all, but the design of the firearm. An example in how it relates to me (others may vary) is the difference between the SA Hellcat and the Sig P365. Though I enjoy several of SA offerings, the Hellcat is not one of them. To me the gun wants to roll upward a lot compared to the P365 making it harder for follow up shots. It is the design that makes it poor for my use...the cartridge is just fine.