Goths- Make huskarls as cheap as goth condottiero and give goths supplies for the champion line and make supplies an imperial age tech

which is as it should be. the civ should have a weakness, and if you’re going for quantity, the weakness is quality. if they had great quality too, the civ would be almost unstoppable. the only civs who could beat them is a civ that has an insanely strong infantry unique unit or cavalry unit that resists halbs.
so basically your options are vikings, aztecs, japanese or byzantines.