The 5.7 really ins't that popular when you look at just how few countries are deploying it in large quantities. A couple of Euro countries have large scale deployment otherwise it seems to be a special purpose weapon for the most part.
Armor penetration is not a valid consideration for any handgun round. Modern armor, even in soft versions is very capable of stopping any of the listed calibers. Even the miracle 5.7 can't get through a level 4 soft vest and still be capable of doing a lethal amount of damage, let alone any grade of hard armor.
The 9 is simply the best choice caliber wise. As previously stated there's droves ammo throughout the world and it provides the best weight to capacity ratio. I do believe our service weapon is in need of upgrading as is our choice of service round (115 gr FMJ's suck). But neither of these things will happen anytime soon so why not focus on maximizing what is available rather than dreaming about what's not?