If you'll look at my posts, I didn't say that it held more powder. I'll have to measure the two to know for sure and to do so I'll have to dig up some 10mm cases. The original published data for both cartridges was very optimistic.
I've owned over a half-dozen 10's over the years, shot it quite a bit and reloaded for the cartridge a bit. I don't think that qualifies as a dismissive attitude. The .357 is not my favorite cartridge. I find it kind of humorous that the 10 is touted so highly as a trailgun cartridge, especially where bears may be a concern, yet the .357 is almost universally met with at best a yawn. The platform of the cartridge is what makes the 10 attractive at all in my mind, besting the .357 in firepower, in most instances. It's downfall is simply it's lack of popularity. It will fall out of favor again soon, I would guess, much like the .41 Mag. has went up and down over the years. Many great cartridges. Many less popular ones. I like stuff that is readily available, the older I get. After brief flirtations with the newest big thing, I always find myself coming back to the classics.
The 10 is a great cartridge that never caught on much to the chagrin of those who espoused it. It's descendant, the 40 did, and there are reasons for that even though many can't see them.
