Agreed. I built my 7" barreled AR 9mm pistol with my wife in mind. Unfortunately it's kind of a hog, not nearly as light and handy I my SIL's CZ Scorpion. The upside is I have a bottom loading Hahn block and I can drop the block and throw on another upper in .300BO or whatever pretty easily if I want. Win Ranger 127 +P+ clocks 1306 out of it and it eats them like candy. Actually it's ran on every single load I've tried in it from USPSA gamer loads to the +P+ with a lone exception. It utterly refuses to run bulk Wally World Rem 115 JHP. No biggie. I should just part it out and go with a .300BO like DocGKR mentions. Rifle caliber...It's definitely a better route for the AR platform. As for actual defensive purposes, sure they will work, but a CZ or Sig platform is probably better suited if you want a pistol caliber.
As far as my PCC gun goes, my 16" JP barrel just doesn't do anything really exceptional velocity wise. That works in both directions too. If I want to get down close to USPSA 125PF I have to load some really lightweight bullets as backing down the already meager charge of uber fast powder just doesn't have much effect. My minor loads running 132'ish in pistols are clocking well into the 140's in the PCC. Having two loads for USPSA is no bueno for me, it's just not worth the effort. I may have to chrono the +P+ out of the 16" just for giggles, but I just don't think there's enough powder capacity in 9mm to see much gain. PCC is just a game, there's not a lot of "practical" use for them other than getting in some trigger time and playing the game.