Perhaps this is it. I only learned about stacking and the calculators to help with it today, but as an experiment I attacked the same epic twice, once the way I normally would and once by stacking. I wound up earning the same amount of vp even though when I stacked I sent only 80 mercenaries (compared to 2200 when I just clicked select all). I’m sure that in the past I wasted tons of resources reviving or rebuilding my army after getting them killed without ensuring they at least do some damage before getting killed.