Radovan is letting his bias influence him.
We fight against and alongside several Garlean gunblade users in game, and they basically never just use it as a gun with a sword attached. Gaius, Regula, Vitus quo Messalla in the 70 job quest, none of them employ a style like a Gunbreaker, but neither is it quite so simplistic as Radovan implies.
Describing what he's holding there as a primarily a gun with an extended blade just feels entirely wrong. I'm pretty sure I remember him using it to summon a magic tiger or something at one point too.
I mean look at him, who doesn't want that as a heavy melee DPS job? With that awesome looking Imperial armor as the artifact set. I wanna learn Regula style sword fighting.