I always took one main weapon and a pistol for backup. It was very rare for me to have to pull up the pistol to finish off someone….but its like health insurance…better to have it and not need it than needing it and not having it eh?. Now I can make more money consistently and im beginning to take SMGs as a second main gun for tight spaces on open maps like resort interior or dorms if i plan going there since the AK74M I usually use can get a bit unwieldy in tight rooms/halls. Thing is, seems to me like if i have a mp7 or mp9 as backup having a pistol that will now see even less use is a waste of space (and money if i get killed..) Both can be drawn while running, both draw at the same speed, and while running with a pistol drawn is a bit faster but not enough to justify preference over pistol, i tested running from A to B and it was about a second in difference with a pistol and a SMG drawn.
TL;DR I think that carrying a pistol is a waste if you are carrying an SMG as second weapon along an AR/DMR