They sure as heck can make it easier, but they were invented to reduce the overall load out of the average soldier. Instead of 12 mags for a 240 rd battle load out, they carry 8 (or more). AR's/M16 started being issued to some troops with 20 rd mags. That was soon changed to 30.

Someone with a reasonable amounty of training can do a mag change, or tactical mag change in a matter of 1-2 seconds. Tactical's take longer.

My duty weapon held 11 rounds of .40 S&W. I had 2 additional mags at all times minimum. During training classes I carried as many as 6. I kept right up with the guys shooting G22's and G23's, both in round count, time, and accuracy. Limit me to 1 round mags, and yeah, that would make a difference.

Someone intent on doing harm to others will generally succeed, regardless of the law or limitations on weapon choices.