Baal is a prodigy who was raised to become another demon noble on par with the 8 strongest demon nobles. He was destined to be great. He has an innate talent for mana manipulation that enabled him to master the fusion of sin energy and mana when he was just a mid-rank demon. He was already a high-rank demon when Infernox was a mid-rank demon. And he wasn't some ordinary high-rank demon either.
He believes he should be superior to Infernox in the ranking since he has the advantage of age, talent, and most importantly, strength. It is nothing personal. It is simply in his nature to lust after good things regardless of whether he deserves it or not. So they will duke it out and see who gets to be the head and who gets to be the tail. Strength should be the determinant of the rank in the house instead of the time you joined the house.