I think the differences between minion (not Balrog) and hero are well balanced, since minion has MP sources with lower MP's, almost no way to actively use Avatar etc. This is compensated by the GI enhancers (Sauron/LE/Bade to Rule), so he can get as much MP's per turn as hero by having more chars in play (hence the 6 starting char limit) and playing more MP resources in one turn.
Balrog is another issue as it is clearly unbalanced. Active Avatar being able to accompany other chars would be enough, I see no reason for allowing him to have such char play advantage.
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