@jojo1 The kingdom has a "court rank" system separate from the peerage system. The court rank goes from 9 or 8 all the way up to 1. Generally most Knights/lords and Barons hang around 9 or 8 for their entire lives, and it takes several generations for a family to climb in court rank.
So Leon who's supposed to be around 8 or 7, cause of his adventuring has shot up past 6, which is outrageous by the court's standards. He's still a Baron, but that might or might not change, I haven't read the novel so I don't know for certain yet.
Put another way, remember Kimetsu no Yaiba? There's 12 Demon Moons, divided into Upper 1-6 and Lower 1-6. Leon's rank went from something like Lower 8 to Upper 6 out of Upper 1-9 and Lower 1-9.