Median is definitely harder than vanilla but normal diablo is nothing compared to some of the challenges that lie ahead.
I honestly have a hard time understanding how you are not able to kill normal diablo with this build, especially at level 60+ with the stats you mentioned.
I recently started leveling a summon nec with widowmaker mixed in just for fun/testing and normal diablo took like 3 min to kill at level 41 with pretty much no gear and around 20 fire res. I uploaded a video of like half the fight showing "build" and strategy, maybe it helps. also notice that town portal wasn't used in the footage.