The main benefit of sword + pistol is to attack faster with a one handed weapon. If you dual 2 weapons, you will attack once with your main, then with your offhand etc, whereas sword + pistol will attack just as fast, but with your main hand only. So if you have one good sabre its better to use that with a pistol than to dual wield good sabre + normal sabre.
The main benefit of dual wielding is using "full attack" abilities, which let you attack twice. For example, the dual pistol build is good for the paladin, because he can shoot both pistols after reloading while using flames of devotion.
Sword + pistol on the other hand is better on classes that have many "primary attack" abilities (monk, fighters' knockdown and clear out).
IMO the best "pirate" build is the helwalker/fighter with sword + pistol:
- helwalker make him squishy, but allso gives him very good damage. The squishyness is however offset by fighters constant recovery, which is huge with helwaker might bonuses
- good combat mobility with long stride (+ fast runner if you want for 40% movespeed). If you get too low, run away and regen while shooting with your pistol
- when you reach level 10 your buffs and debuffs last forever with duality intellect modal
- lots of "primary attack" abilities that have good synergy with sword + pistol style - For example, the monks force of anguish strike will knock the enemy away, then you can shoot him with your pistol - you can also deliver stun attacks from range which is nice. If enemies gang you, use "clear out" and run away.
tldr; sword + pistol good for fast attacking with one handed weapon, fast delivering "primary attack" abilities. Flexible without having to switch weapon sets and suffer recovery from that.
By the way you can cancel the reloading animation by just clicking on the enemy again. He will switch to his melee weapon and strike instantly