I am not there, but that's around the level where Kripparian said the "bad" starts to creep in, in terms of overtuned difficulty. Especially in perhaps 10 or so levels.
It's where "builds" go to die. Up to early maps, you have tons of variety and options, but once you push past maps 5+, you hit a brick wall unless you stack every node on str and focus on every defence passive you can. Because the damage of mobs, and the hard hitting abilities, goes up to such a degree that you get oneshot like mad. Where one pixel will matter if you get hit, and that hit will more often than not oneshot you on boss maps. So you lose 10-15% exp, all map progress up to boss node, and the boss node. So Kripparian said at that point, unless you're really good, it will become really hard to level up, and also progress.
Only "melee" builds I've seen Ziz do there is where melee is a loose term. More totems and massive AE strikes. If not it's hit once, then run around and dodge, then hit once. However, it becomes a very big challenge since one mistake in between those hits usually means death and you spend far too long on the boss since you can't DPS and spend time evading everything.
Ziz is doing a witch infernalist build (hardcode), but stopped and grinded at tier 5 maps because he wanted to change his build to incorporate 10-15k energy shield before going to a higher tier due to DPS increase from mobs and their abilities.
