I actually found the opposite, Act 1 was moderately difficult depending on encounter, some encounters were difficult beyond reason (the Undead Casters ignoring your magic armor to cast rain (wet) + ice spell (instant cc through magic armor and all resists)), but the majority were reasonably balanced.
Act 2 was relatively easy for me, I did all of the Reaper's Coast without having more than a handful of deaths. The abomination was rather difficult for me to kill, the one that has 50% permanent lifesteal, 8 action points a turn, and a horde of minions, it took me a couple of retries to cc him and keep him cc'd. The Witch-encounter I never really beat, she repeatedly oneshot me with aoe abilities, probably something I was missing though, not much of an issue. I was able to do fights that were 3 levels above me with relative ease, on Classic.
Act 3, Arx, on the other hand was terrible. The gear I had that was otherwise on level on the Nameless Isle was completely useless, it was all hundreds of armor points in value down. Enemies that were a level above me were unbeatable. Reaching level 21 allowed me to easily beat all of the encounters on classic while asleep. At level 19 they were all unbeatable, for my set up at least, at 20 they were relatively easy, at 21 even the level 20 encounters were very boring.
There definitely is a stat issue, and general pacing issue after Act 2. I uncovered almost no new spells after the end of Act 2, and honestly never bothered with the crafting or spell crafting...they felt underdeveloped. The extreme limit with Spell Crafting, along with significant difficulties using the crafting system (limited only to crafting chest-pieces; I never used grenades or scrolls, the system was never put in use by me), I just never found a use in it.
That ultimately led to a significant stagnation after the end of Act 2, I liked the Nameless Isle, for the most part, the Godwoken Academy at least, but the pacing was kinda poor.
The fights in the third part of the game were kinda poor. The doctor was wiping my group with his unlimited source casting, blowing away my entire team's magic shields with a single aoe spell, before having one of his minions immediately use a charm, and another cast horrific scream to cc my entire group to death.
I do feel like, while the majority of the game was great, they didn't properly test the final part of the game.
