I'll chime in on the issue with support for using lighter ammunition to get the new shooter up to an appropriate skill level before switching to heavier loads. Unfortunately, while this spectrum is very wide for revolvers, it isn't for most automatics.
The dilemma diminishes somewhat, as bore diameter falls either side of .354" - .358". If the projectile is greater than .358", appropriate weight for the bore, and operates a stock slide with a stock recoil spring (or reliably exits the revolver barrel), the load is probably adequate for defense, no matter how "shootable" or "un-shootable" it may be for the shooter.
If the bore diameter of the piece is under .354", no load that won't soon wreck the pistol is really adequate for defense, despite the anecdotal spectacular results about which we sometimes read.
In the 9mm/.38Spl/.357Magnum range, the projectile's mass, velocity, and configuration may make a world of difference (excluding the .380 A.C.P. and 9x18 Makarov, which are just too anemic). If I was constrained to carry a 9mm for defense, I'd certainly feel better equipped with a 125 gr LFP at 1100 f/s or a 147 gr. of similar configuration launched at over 950 f/s, than with 115 gr. FMJs launched at 1250 f/s. Ditto the 9mm Largo and .38 Super, though finding these in anything but FMJ can be a chore.
Personally, I use 200 gr. RNFPs or SWCs pushed hard in my .45 ACP to ring a metal gong at 100 yards. I use 250gr. RNFPs pushed hard enough to reliably operate the slide, to kill bowling pins. I use a 225gr. (228gr. as I buy them) Lee TC over 6.0/Unique for everything else. I would not feel ill-equipped for a fight with ANY of them, at customary pistol ranges.
For eons, the factory .44 Spl. load launched a 246gr. LRN at just under 700 f/s. Judicious reloading, and better factory loads somewhat improved this performance. I doubt that felons shot with any of these loads could have told the difference among them, but the shooter just might shoot one load better than the other.
Since hits are what count, the load with which the shooter connects in the vital or head zone most often are probably what they should use, but if there are many, pick the one with the greatest momentum and be done with it.