It's like comparing disk brakes to drum brakes. :/ They both stop the car, but they go about it in totally different ways.
To be accurate, for the M-16, it's magazine.. :/
For the record, I think a Glock with a 30 round mag is pretty danged silly.. I wouldn't want one.. Too bulky for one thing. And all that ammo adds extra weight.
But saying that, having an uber high capacity mag is not going to make one much more dangerous than another carrying several factory mags. It's up to the shooter's capabilities. Many using stock mags could probably put AZ whack buoy to shame if it came down to a contest to see who could get off the most rounds in
60 seconds. I have four mags for my usual device, but I never load more than two at a time when I'm using it. Just two mags is 29 rounds counting one in the chamber with mine. That's more than I'll ever need for defense purposes. If I were a cop, I'd probably carry all four though.. :/ Better safe than sorry when fighting crooks, deviants, and whack buoys.