Watch some youtube videos showing bullet penetration and expansion into various things like calibrated ballistic gelatin, water bottles, or tannerite (lol) to see the differences.
When comparing i.e. .223, compare 53gr ballistic tip varmint ammo vs 55gr fmj vs 62 gr SP vs 68 gr OTM.
Doing what a gun is "for" at what distance, accurately, is the big factor in handgun vs rifle (to me).
Handguns are used defensively at short distances. The ability to hit the necessary target when under stress or on the move is as much if not more important in a life or death defensive situation than actual bullet energy.
Usually if you have a rifle it's for an intentional use like hunting some known thing in some known environment, be it a squirrel at forty yards or an elk at 400, and everything in between.
Range, target shooting and other games excepted.
All generalizations are false. I am not a lawyer and did not stay at a Holiday Inn Express last night.
What do you plan to use it for?