The .40 is designed to shoot a bigger, heavier bullet at faster speeds than the 9mm can. The whole kerfuffle with 9mm isn't that it's a superior cartridge to the .40, it's that it's cheaper to shoot, has less recoil in smaller pistols, doesn't wear out the same sized frame pistols as .40 does, and it's not "that bad" for defense.
I can agree with the first three points, but never have I read ANYWHERE that said 9mm is superior to .40 S&W.
Anyway you look at it, 155, 165, or 180 grain, the .40 S&W respectively beats the 9mm in 115, 124, or 147 grain. If all you want is a "get off me gun" or something at point blank range, then sure, you don't need a .40 S&W and you may not even need a 9mm either, .380 will do the job, but if you want something that can punch through barriers, something law enforcement and federal agents are required to do time to time, the .40 S&W is still the better choice.
The .40 S&W was originally created to push a 180gr JHP upwards of 980fps. A little heavier bullet than the typical 9mm of the period (147gr) and with acceptable sectional density.
Over the years the cartridge has been in-service there's been a bit of experimentation with lighter bullets weights for duty loads, but in recent years the emphasis has gradually returned to the 180gr bullet weight in LE/Gov use.
The 155's used by one major fed agency were somewhat rough on both guns and many shooters, and when it was eventually (briefly) replaced with a lighter 135gr JHP, that load was "down-loaded" somewhat, compared to similar bullet weight loads available over the counter. It was specifically ordered to run 1200fps, with an allowable +/- of 50fps (meaning it could vary from 1150-1250fps). (Again, the 180gr bullet weight has been making a significant comeback.)
The 165gr bullet weight has been produced in both "standard" and somewhat reduced recoil (reduced velocity) versions for LE users over the years. It's also been a popular alternative load for consumer sales, too.
Yes, the .40 is harder on guns (and many shooters) than the 9/.45, but that's more of a maintenance/support issue, and newer models have been designed around the caliber, instead of having been modified from existing 9mm guns, as in the early days of the caliber.
Yes, in recent years there's been a growing segment of LE users transitioning from using .40's to using 9's, and many proponents list addressing training issues (initial and recurrent) at the top of their list of reasons. Naturally, most armorers won't mind a little less wear & tear on the weapons they support, but again, the newer models designed around the cartridge have been making those chores easier, too.
Now, I presently own 5 pistols chambered in .40, and I've carried 3 issued pistols chambered in it, too. I've invested enough time in the caliber in the years I've been using it (since 2000) to have fired some few ten's of thousands of rounds of it in the various guns I've used, as well as some training guns.
I own 6 pistols chambered in 9 and 9 pistols chambered in .45, though.
I even own more 5-shot snubs (.38/.357) than I own .40's.
The .40 is a fine caliber for its purpose. Probably not for everybody, but what caliber is?
I've no doubt it'll remain within the top 3 service/defensive caliber pistols calibers for many years to come.
Doesn't mean I'll not carry my 9's & 45's (and snubs) as often, or probably more often, though.
Suit yourself. Just make sure your range time and training/practice regimen support and justify your choice of carrying it, and your confidence in
using it in dynamic, chaotic and fast-paced situations.
It's generally more about the caliber
user, than the specific
caliber.