"200 rounds"

I'd rather have 12 mags of 20 shots.
Too bad I couldn't carry it even if I was pistol qualified...
As far as the Army is concerned, at least. I'm actually fucking good with pistols.

just imagine trying to clear a room with a 4 foot long mag

It would more or less eliminate the key features of a pistol like being concealable, compact, and light. Those features come with disadvantages in range, accuracy, power, ease of use and follow ups, etc. which is why the rifle is generally a preferred weapon for just about everything except killing things in close range in a pinch or when one doesn’t want it obvious or conspicuous they are armed. I have seen pistol drum mags, mostly for Raficas and automatic glocks to function as a sort of SMG/LMG hybrid, those could carry 200 rounds and not make a pistol completely useless, but their size, weight, and effect on weapons handling still makes them more of a novelty than a useful and tactically versatile tool.

Agree, but right quarters are what I was referring to. Open field a pistol is a step above a knife.