Add a feature where the more heat is wasted when heating a item because it's heat bar is full the better the chances are for getting bonuses when using the forge for "that level of that item". This would be a tiny but noticeable tweak that would balance the difficulty of heating stuff now compared to before the update and solve all those suggestions on storing wasted heat without being OP.
I would prefer if they made it so each weapon requires more heat (like 3x more), but each forge level is 100% chance of forging with a higher chance of extra bonuses and stuff the more crystals you add.