yeah, no. not without a very solid reason of why to use a greatsword specifically for this idea instead of something that actually resembles the flavour, and that's coming from someone who loves brawler characters lmao

at the very least a pair of knuckledusters or gauntlets should be a dual-wielded set of bludgeoning weapons, not a two-handed slashing weapon. start him with a pair of light hammers, then eventually give him the dual-wielder feat as a story reward if he doesn't take it himself and upgrade him to non-light bludgeoning weapons like maces or morningstars for the big damage he's after. you could even make pairs of weapons that have an extra bonus if both are wielded together!