Well it took thunder king 30 days to beat an average wild god xuen who is either same power level or weaker than cenarius and during wc3 how mannoroth talked about cenarius saying he wishes to face him again would imply that they fought against each other before and either they were similiar in strenght or mannoroth was stronger and players defeated mannoroth without help in wod who was being helped by Gul'dan and at final phase mannoroth was empowered meaning stronger than nornal.
putting players in wod at lk arthas level as a party.