I think it could be great to have a new display during a monolith run that shows the amount of ennemies in this run and also shows how many ennemies that have been killed. Just under it, displaying the loot bonus for the reward chest would be perfect !
When I first started playing, one of my initial questions was if clearing made any difference to the MoF runs & loot chest content. While there are other issues with MoF, just giving this kind of feedback could “give the illusion” of having something more to do on MoF runs.
This, together with some proper explanation tutorial, that clearing more monsters does increase the loot from the chest would most certainly be a valueable addition to this game mode.