First of all - I think you should understand that different people have different needs and requirements. F.e. I require high expansion and deep penetration (relatively deep, so the bullet won't be stopped short by a minor bone, f.e. 16") - this can be achieved via v. high velocity 125gr bullet OR by firing a subsonic 180gr bullet with a lot less flash and report.
I consider .45 ACP the best handgun defensive caliber BUT in revolvers high bullet diameter = lower capacity OR higher diameter of cylinder.
So in revolvers .357 Magnum is pretty much the best compromise between bullet diameter and capacity/weapon size. And .357 Magnum, thanks to the overal length can fire both light and v. fast bullets and slow and heavy bullets. Slow and heavy bullets that can succesfully mimic .40 S&W or even .45 ACP performance, but only with a properly designed bullet.
Unfortunately, .357 Magnum's potential is not really fullfilled. It's being shoehorned into a "turbocharged 9mm", and it wouldn't be that bad if its 125gr bullets were really as good as f.e. Ranger-T or HST 9mm. But they're not.
he 230gr bullet is not heavy for caliber in the .45 ACP, however a 250gr bullet is.
It's v. heavy for a HOLLOW POINT. The fact that you can squeeze 250gr hardcast bullet into .45 ACP case doesn't make 230gr HP light. Just like 180gr is the extreme for .357 Magnum hollow point - hollow points are lighter by design - and around 200gr HP is pretty much as heavy as HP gets in 10mm.
You're claiming 125gr bullet is "the best". There is no scientific evidence confirming this statement. Nowadays 125gr bullets don't expand or penetrate any better than 158gr or 180gr, thanks to progress in bullet design. 125gr USED to be the best back in the days of hollow points having problems expanding at lower speeds. v. high speed of light 125gr bullets allowed for reliable expansion.
Nowadays we have way better bullet designs, f.e. 147gr 9mm bullet that expands at subsonic speeds to a larger diameter than most .357 125gr bullets.
It's a fact that there is VERY limited self defence bullet selection above 130gr in .357.
It's a fact that in 10mm you can choose from VERY wide range of SD bullets from 135 all the way to 180-200gr.
It's a fact that faster bullets produce more report for a given diameter, which is further amplified by f.e. confined space - which means that 125gr .357 Magnum is NOT the universally best SD cartridge available and there are situations where slower 158-180gr bullets would be better - too bad there isn't really a lot of these to choose from, while 10mm/.40 S&W gives you plenty to choose from
And really, what do you want to prove by using Underwood ammo that simply pushes the bullet as fast as possible - so there is little difference, because at 1400 fps the bullet expansion is taken to the extreme. The idea is not to produce as much report, flash and recoil as possible, the point is to get the best effect at normal velocities. In case of 10mm ammunition you have more options and way more modern bullets in different weights. In .357 Magnum you once again get LESS expansion than from 9mm, with a lot more recoil, report and flash. What's the point? The main advantage of .357 Mag over 9mm nowadays is that .357 can use a LOT heavier hollow points.
This advantage can be translated into v. good expansion and good penetration without too much report - like in case of Black Talon. Unfortunately, thanks to people like you, ammunition manufacturers are not interested in using full potential of .357 Magnum.
So, to make it simplier for you to understand: in 10mm one can CHOOSE what kind of bullet he wants. In .357 Magnum you have no choice, you either choose ear-splitting 125gr loadings, or you're limiting your choice drastically.
Of course you can keep claiming that the less choice the better and that 125gr .357 Mag in some magical way is superior to everything else, even though most 125gr .357 Mag bullets expand less than 9mm counterparts while producing a lot more noise and flash.
So, to sum it up:
10mm in revolver is a lot better if you want to choose from a wide variety of bullets, from v. fast and light, to heavy subsonic.
.357 Magnum if you don't want to have a choice.
How is not having a choice better?
I don't know, maybe you should explain.
Not saying the either is a bad cartridge because they're not, but at the end of the day it all really boils down to what one like best. Just like me and all the other .41 fanatics out there.