While the difference between the .380 ACP and the more common standard pressure and +P loadings in .38 S&W Spl can be discussed, I tend to include the "shooter" aspect in any discussion I'm having with someone looking to decide upon a smallish off-duty, retirement or CCW type weapon of those calibers.
How well can the individual do with either type of handgun in the first place, meaning shooting a diminutive revolver or pistol?
How well can they manipulate it & load it?
Can they carry it safely & securely in their normal circumstances and activities?
Can they safely, smoothly & effectively draw & present it?
Can they maintain it (properly inspect, clean & lubricate it)?
Once they've decided upon whichever platform is actually going to be carried, then we talk about ammunition.
I've seen folks using examples of each type of little handgun who would have been better off using the other type. Or spending a lot more time on the practice range. Or both. Depends on the individual ... meaning their knowledge, foundation skillset & abilities, as well as their interest and willingness to develop & maintain their skills.
They've got to actually hit their intended target before the "effectiveness" of the caliber can come into play, right?
Me? I've handled and fired a pretty fair number of .380's over the years.
The only one I ever owned was a Beretta M84 (which I sold off not that long after buying it). While they make a growing number of diminutive .380's nowadays, I choose to own half a dozen S&W J-frames. (I'm also a long time revolver shooter and longtime pistol shooter, so I have some experience using each for my needs.)
Having 5 rounds versus 6-7 rounds isn't something that concerns me, overly much, for my perceived needs and use.
I don't expect everyone else to use my reasoning for their selection process, though.
I tend to think folks ought to suit themselves, and their individual needs, based upon careful decision-making and prudent reasoning. Caliber might be part of that reasoning, but I wouldn't expect it to necessarily be the primary reason for everyone.