By the way, you kind of contradicted your own weaknesses in your own post
I see what you mean, and I'll explain what I meant.
The easiest way to do so, is to compare with other weapons.
9mm - less than half bullets in clip compared to bullpup, slightly weaker, worst iron-sights, lower firing rate. No wonder it's the starting weapon.
Handcannon - 2 less bullets in clip compared to LAR, slightly weaker, higher fire rate, , high recoil, worst ironsights.
Dual 9mm - still has less bullets than bullpup, still deals less damage, arguably higher accuracy, on skilled hands has almost the same fire rate.
Dual Handcannon - 6 bullets more in clip compared to LAR, still weaker, even higher fire rate, higher recoil, almost no accuracy at all compared to LAR.
Revolver (if added, this is how I expect it to behave) - 2x M14's damage, bullet piercing (same as HC), inhuman recoil, average ironsights.
As for my contradictions, here follows the specifics
Ammo:
Two times a small number is a small number. Just take the Handcannon: 8-round clip, times 2, leaves you with 16-round clip. Sure, the LAR deals just a little more damage, and has 6 bullets less... But you ain't hip-firing with a LAR, and with a handcannon, you HAVE to.
Accuracy:
Average ironsights means you can hit at longer ranges, but the very ironsights get in your way. Bullpup, SCAR and Crossbow have excellent ironsights, and the LAR has great ironsights. You can hit at long range with any weapon, provided you aim down the sights, and you're used to them.
Damage:
A Gunslinger's weapons deal below-the-average damage and/or have slower firing rate; a high-DPS rate, for a GS, is a medium-DPS for other perks. So, when I say "high single target DPS", I mean the highest the Gunslinger can reach (which is with dual handcannons).