Actually, no, Mace could well solo. Nihilus' poor track record with Drain, Mace's Vaapad being able to reflect the powers of a greater Force wielder than Nihilus in Palpatine, and the recent revelations regarding Nihilus' TK honestly make me inclined to favour the Korun over the Lord of Hunger. It helps that Mace can be scaled to being well above Traya in power as well.