One thing that may really help from what I have read here is doing what we did in Descent 1st edition (and will probably start doing here as well after this questline) is to randomly select your Heroes or even better do it Relic style which is radomly selecting two, then pick one, then repeat that process. It just sounds like the combination of Heroic abilities you've described is what is making the issue and random selection would (especially since you have the conversion kit) greatly reduce the chances of always having to deal with those combos.
For anyone concerned that the OL is too powerful, you can also have this apply to the OL as well. In fact, I would recommend that if the Hero players are forced to choose from a random subset of heroes (and possibly classes after you pick up some expansions), then the OL should have to choose from a random subset of his available open groups in the same fashion that the hero players did, treating each open group as a hero player. (Simultaneously vs. one then the next; a set number (e.g. 2 or 3) vs. a proportional number (e.g. half, evenly divided); etc.)
Also note that if you're going to go this route, then I WOULD advise picking up the conversion kit for the variety since ridiculous combinations are much less likely to show up.
Edited by griton