The 5.7x28 and the .45 ACP work differently.
The difference is a lot like hunting with a .30-06 vs. a .45-70. Either one will bring down big game.
One does it with a small, high-velocity bullet. The other does it with a large, low-velocity bullet.
For rifle hunting, a flat trajectory matters. For pistol self-defense, it doesn't.
I'd opt for the .45ACP for self-defense because I WANT the bullet to drop faster and penetrate fewer walls. I live in town.
However, small, fast bullets do work. It's well-proven by a century of hunting.
I am definitely someone who does not buy the "9mm is just as good as .45" line. Elk hunters will tell you that there's a marked difference between .30 caliber 150 and 180 grain bullets, even if the 180 is going slower. There's no way that a 230 grain .45 isn't a better stopper than anything you can load in a 9mm, assuming each has a similar bullet design. Just NO WAY. Too many years of people actually bringing home meat with different bullets back this up.
However, the 5.7 is a different animal from the 9mm or .45, and just like the .30-06 and the .45-70 do the same thing using different means, the 5.7 is an effective round despite its smaller size.