I wouldn't say that, Ramza and Alma aren't really involved with the resistance portion of the story, just the Zodiac Braves portion, and being thespian nobility in exile is kind of the opposite of war orphan street urchins.

I like Vaan well enough, he fit a very important role as the commoner in a grand story. If all the characters were princesses, knight captains, elfin rabbit girls, or nobility disguised as sky pirates it would lose a sense of grounding. He was also important in contrasting with Ashe while they underwent parallel character arcs. Both lost a loved one to the Archadian Empire, both have ideas of revenge against them, and both were being groomed by the Occuria to use the power of the sun cryst to destroy the empire and strengthen the hold the Occuria had over mortals. When Ashe looks at the Occuria-created ghost of her dead husband Rasler, Vaan mentions seeing someone that looks like his dead brother Recks, which is important because none of the other party members can see this figure at the time, showing that the Occura had more than one iron in the fire of who they would make the new Dynast-King.

Vaan's character growth and experiences makes him realize that while he hates Archades, destroying them won't bring his brother back and will only result in more death and sorrow, which finally gives Ashe the push she needs to destroy the sun cryst and keeping the Occuria from ever bestowing its power on those they choose to enact their will.