Yeah I agree, When I load up and see new players in the middle of choosing there characters I thinl Oh man im not about to fuck up your day, nope" so i do what I always do, just watch them succeed without appearing in the stage, and if i do pop in i stay very far away. (Unless im Doldren and ill stay close but never manifest).
So yeah I think in mentor matches Antags should be disabled until they can hold there own and have a feel for the terrain.
