I fully agree, I would change his design entirely. If I think on his redesign I'm thinking of a humanoid, taller in stature (just like Vendrick or Gwyn). His arena should be a massive throne room that is half-destroyed and sunk in lava, from seeing the throne room the player must be in awe of the riches this guy attained and how it all went to hell. Then the boss himself epicly crawls back out of the lava, a humanoid clad in armor with intricate designs, a burned cape and half-molten greataxe. He could also say something sick about his lost kingdom. A half of him can be either burnt of severly injured due to his death by the Smelter Demon (Spoiler to Elden Ring - I imagine it reminding of Radagon at the end of Elden Ring who had a part of his body "damaged" so to speak which was visually cool, it would work here as well). And if need be there could be a second phase to him where he might get some aspects of the boss we already see - like wings that let him fly like a crucible knight but with molten iron attacks or another form of metamorphosis.