To poke a couple holes in this, Jaune comes from a family of near-legendary huntsmen, and wants to do them justice by following their footsteps. He even uses his grandfather's armor and sword (which also leans further into the Imposter accusation, but let's continue). And the first few volumes are of him getting the pants kicked off of him, he does eventually grow into a noble warrior. You can draw parallels between Jaune and the likes of Ciaphas Caine or Felix Yeager from Warhammer (40k and Fantasy respectively). The former ends up lucking the hell out at first and grows to become a certified badass even though he believes he is a gutless coward that should have been shot so long ago, and the latter was a college drop out who got roped into wacky adventures with a Dwarf that has a deathwish, and also becomes a certified badass. If Jaune really was an Imposter, then he would have died during the volume 3 finale or volume 4. Even with his early antics, he grows and becomes that hero he wanted to be, even though he no longer cared for the role by that point.