I know this may be extremely late, so I'm hoping that you'd have at least found another friendlier server, or at least have had a better run with both classes.
Regarding Gunslingers. Gunslingers are not Archers - it's an easy mistake, but that's the fact. They have five weapon types, each with their own speciality. Grenade Launchers are the only weapons which ammunition is elemental - excluding Endows. Rifles are for their Critical Hit bonuses and Tracking, which allows you to hit ANYTHING in the game. Gatling Guns on the other hand is reliant on high attack speeds and as such large unwieldy weapons go, require you to fight from a distance. In PvP, people favour Shotguns and Handguns because they are the best source of damage for Gunslingers.
In response to your complaint of the lack of weapon attack power in Handguns, I'd like to assure you that the damage comes from the damage bonuses from cards, various items, and most of all, the Skills. Among the non-transcended classes, Desperado has perhaps the greatest damage potential in the game.
Ninjas are a something else. There are three major types of Ninja builds: Magic (aka Ninpou), Throwing and Final Strike (Issen). The first is utilises Blaze Shield, Raging Dragon, Lightning Spear, Hidden Water and Kamaitachi. Throwing Ninjas with fair amounts of AGI utilise Shurikens and Kunais; due to their focus in STR, some also take Final Strike as an optional skill. Final Strike Ninjas focus on STR and Max HP for damage, maybe a small amount of DEX for the optional Throw Shuriken.
I'm not sure how much satisfaction you've found from your "melee" Ninja, but by now you'd probably notice the deficiency of melee support skills. Which is rather in-character, if you think about it: Ninjas never stand face-to-face with an opponent. They fight from a distance and from the shadows.