The issue is the u50 nerfs disproportionately effect different damage styles. Optimized melee DPS got a 20-25% nerf, optimized ranged DPS got 18-23%, optimized caster DPS took a whopping 30-40% hit. These are raw damage values assuming you always hit and no fortification, so it's actually much worse in practice. DPS casters really are in a "just reroll something else" place after u50 because pre-u50 caster damage was balanced around spell power / spell crit due to every spell hitting MCL almost instantly at 20. Post-u50 is the same, every high end spell is already at MCL so the only place to draw power is spell power / spell crit and the combined nerf is ridiculously large.
This gives them three "options", adjust the monster HP at cap by 30-40% making it neutral for casters but a very large buff for melee / ranged DPS, which makes DPS casters obsolete. Adjust monster HP by 20-25% making it neutral for melee / ranged DPS but a huge loss for DPS casters thus making them obsolete. Adjust the HP by less then 25% making it a nerf to melee / ranged DPS and an even bigger nerf to DPS casters making them obsolete. Remember this is at cap not leveling through heroic Sharn, at cap DPS casters are already at a loss for damage but they can hit multiple stuff so it kinda balances out. That's history after u50.