I have a noctule sin (not batstrike) who does pretty good dmg and has good def, but after I killed diablo and got to harragoth I took one step outside and got completely destroyed but a million rare monsters and invisible birds and shit. I can make it through if I'm careful about which monsters I rush into but jesus christ man hatred never had a big difficulty jump. This game never ceases to surprise me with its random difficulty.
I think he's more referring to the difficulty jump from acts in terror as you progress more than struggling with the build. I had many issues with my barb in a5 terror too and had to stop him for a long time