My personal thoughts on this is that yes, handguns are weaker than rifles, but often strong enough to get the job done. However, the thing with handguns is that the different common SD calibers (38spl/9mm through any 44/45 caliber) are all very similar in how well they can stop a threat. However, the difference between a round nose, lead or FMJ, and a premium hollow point is actually bigger than the difference between most calibers (unless you're accustomed to carrying 454, 460, or something similar).
Like 44AMP said, since the only way to for sure STOP a threat (not necessarily kill it) is to incapacitate it, then as long as the penetration is still enough to reach the vitals of heart, lungs, or brain depending on POI, I would much rather have a HP of some sort that could open up from .35"-.45" to .5"-.75" depending on caliber and gun used than a round nose/FMJ that doesn't. This gives you a much larger margin of error in the accuracy department when it comes to hitting a key component of the central nervous system.