Essentially they could just move the chests to the boss room and they unlock / pop up after defeating the boss, ending up in a shower of loot which could solve the problem (and of course probably end up creating another where people just find a different, more efficient manner of collecting loot). Of course smaller mobs would still drop loot, but the better loot coming from the chests.

TBF i see why this is a game ruining experience for players, but it's mainly on the fact that they made bosses not worth doing for those who maximise on loot efficiency. The game will always have those who want to min max their loot efficiency and will find the methods to do so, so it's up to the developers to figure out how to make it so it doesn't ruin the experience of non-min maxers and still allow min maxers to efficiently gain loot.