Everything else you describe is true except this- a 147 JHP would NOT be a vast improvement in lethality over 124 grain NATO Ball. An improvement yes but not enough to matter given the sorry state of pistol skills in most general purpose forces.
The only thing that would provide a vast improvement in handgun lethality would be improving the soldier or marines ability to hit relevant (B-8) sized targets at speed and under stress.
We have a hard time doing that in LE and handguns are our primary weapon.