Vartans are the base class for Hawkman and Canopus. Their obvious advantage is the fact that they can fly, and have very high base move. This gives them unprecedented mobility on the battlefield. I'm not sure, but I don't think that's a class ability, so even as an Archer, Canopus should still have the same (or close to it) movement, so it's a moot point.
Their big advantage over other classes is their 'El Colas Winds' ability. This gives the caster and nearby allies Air-Touched, and Truestrike. These two buffs are what bumps the class past just straight damage output, which is what the Archer excels at.
If all you're looking for is damage, then yes, not much beats an Archer for that. Vartans, however also have the ability to use melee weapons, and one-hand bows. They're meant more as a generic, fill-any-sort-of-role type of class. Need to plug a hole in the formation? Send in the Vartan! Need a bit more ranged damage? Pull him back, and let loose with the bow! They also make excellent decoys, as their avoidance stat can go higher than any other class. Since enemies tend to focus on weaker enemies, a Vartan is usually pretty high on the priority list.
It's happened many times that enemies gang up on Canopus, he dodges, and promptly counterattacks. A single hit, by itself, won't match anything else damage-wise, but add in several counter-attacks (with Air-Touched!), and you might just find yourself out-damaging the Archers in your group.