I don't think I'll buy those theories. I carry a .45 auto. Ball or JHP will be stopped by armor. True armor-piercing handgun ammo is illegal (thanks to a BS expose launched by NBC years ago, that resulted in the injury and death of a number of cops shot by goblins who watch TV).
I generally like full weight bullets. In .45 it's 230 grain. I like Hydra Shok, but would carry any good JHP that's reliable in my gun. In .357 or .38 I might go as light as 125 grain, though I like good old 158 grainers in the field.
I have been known to be a bit short of premium defensive ammo when about to go shopping down in "civilization" (just slipping on a 1911 is fine at home, but a couple of extra magazines seem appropriate when visiting a city), so I'll grab a couple of magazines filled with ball. They are all 230 grain and jacketed, landing in pretty much the same place on a target. It's not that I'm mixing intentionally, it's just a case of grabbing what I have - and .45 bullets are pretty big even when they don't expand.
If I was a cop and in a service where shooting at a barricaded suspect or one in car seemed likely, I might carry one magazine of KTW, but in general I see no good reason to mix ammo. That business of mixing to accomodate different outerwear would only make sense if you were carrying low penetration ammo like the lightest Glaser or MagSafe; and that stuff doesn't make much sense except in special environments like that of a Sky Marshall.