Well you actually do less damage using a greatsword over dualwielding anyway. Greatsword adds 3,5 damage over a short sword but you forgo one or even two offhand attacks leading to lower damage output in a situation where you can spend all your action points attacking.
True, the only thing is this allows rogues to get away with that may help with more damage is taking the Great Weapon Master feat at level 4 so they can have +10 damage and a chance to bonus action attack.
