Have a look at Grimmest if you want more difficulty. You can adjust the spawn rates for mobs/heroes with that mod.
It also included in the Grimarillion mod which would give you more masteries to play with since it adds masteries from Titan Quest, D3 and also a mod called Zenith.
Believe me, even on the lightest Grimmest setting of Alcoholic you’ll often be running into 5-7 heroes at a time.