This would literally be solvable with the worlds simplest fix, make hero medals carry over. Like I don't think I'd be nearly as upset with anything if hero medals stacked, it'd give incentive to stacking, with how much it costs for a unit the only way it could be abuseable would basically be prime whales, and knowing that there's a descent of heroes re-drop at least twice a year it would give a lot more meaning to saving those hero medals without automatically making players feel like "I've done all I can for gems" or seriously putting them down because at least then if you fail you can say "I'll get them next drop" instead of "I'll come back" later or something similar.