I know, for lower tier players Heroics can be a turn off, as they may not have the required characters, but how about you bring them back with all 1, 2 and 3s available for play, with the 4s limited to the boost list only and no 5s available (if you need to keep the 5 node in, then let it be that it’s the only node they can be used in).
Lower rosters can play, vets get to play with their 4* toys without worrying about being at a disadvantage and 4* players have a chance to lean up, as they know how to play those characters quickly.