Large part of the issue is the discrepency between builds. Personally I felt fine as soon as I hit 14, which granted is pretty late in act 1(if you're a speedrunner it's literally on the last boss, for me it was a little bit before). At that point I got Ember Fusillade, and unique mobs and annoying rares started dying instantly with Orb of Storm+Ember Fusillade. Then once I awakened as Disciple of Varashta it was pretty stupid, I pretty much didn't see any of the mechanic on any of the bosses. And by didn't see I didn't mean like when I played vaal guards and couldn't see anything, I mean the bosses just die as soon as their RP introduction is done.
Looking at the speedrunners stuff, you can see large differences between the runs where they use meta shit and have good weapons, versus when they use shitty skills, and that's still with good weapons, shitty skills and bad weapons is just stupid slow fights where you run out of flasks and shit.
I didn't mind the campaign at all on this run, but yeah I barely died and just was mowing down instantly, and I'm still doing that as I'm progressing map tiers atm.
Y
Yaamean
you are supposed to Regal gear while leveling, mostly you want to use a regal every act on a good weapon base if playing an attack build, and otherwise on a +lvl caster weap for spells/minions just to fish for better stats, and extra regals on rings/amulets and stuff you might also want. Exalts too, they're pretty cheap, I threw a bunch on my minion helm when I got it cause I figured I wouldn't upgrade it soon(it's been 40levels). Pick bases up, transmute+augment then regal if you got something good. That and checking the vendors when you hit town. And resists are fairly optional for the first like 3 acts, as long as you have good damage. Make use of the league mech to get artificer orb and resist runes though, it's pretty easy to get resists this league