So, the .40 doesn't do anything that the 10mm hasn't been doing for many years prior to it becoming a commercial cartridge
You mean like fit in a 9mm frame size gun?
I've been enjoying handguns since the early 1970s, and the one US caliber I have never owned is 10mm/.40.
I have, or have had, .22s..25s,.32s,.380s, 9mms, .38s, .357s, 41s, .44s, & .45s. I haven't found anything in my life that the 10mm does that isn't already covered (on either end of any scale you choose) by what I already have.
If you go to the extreme ends of the spectrum, the .357 beats the 10mm in power (although you need a gun that most people feel falls outside the "carry gun" class to get the most you can get, from either one).
.357 beats the 10mm on the other end, firing .38 Specials. Cost is lower for .357/.38 (although for some loads the difference isn't much, for others it is), and the .357 is hands down winner for availability off the shelf ammo.
If you handload, then the point about ammo availability is moot. Cost is essentially the same, with a small difference in the cost of brass and bullets, the 10mm (being essentially still a niche caliber for brass) generally costs a few pennies more...
Simply put, I'm not going to go get a 10mm (or a .40) when I have half a dozen different .357s to choose from, already. But that's just me.
I will say this, if, at some point you get tired of the 10mm, selling one is aiming at a much smaller market than a .357.
Essentially, it comes down to you deciding what gun best suits your needs, and likes, and then choosing which caliber it is offered in that also best suits.