Some suggestions

[Addah]

get mavs from 300 chests -> jump into cows @ 3 hours or so -> ez 99 in 12 hours max

It seems there's a problem of too much XP generally speaking, there's no joy of leveling up when you find a single inferno cow game and reach 90.

If all XP was reduced then it's more likely Nightmare could have the same rate as Hell without imbalancing things.