I wouldn't say Season 3 is more difficult in terms of mechanics. There's an occasional mechanic from bosses that I'd say is "unfair", but I feel like the easiness comes from how long the wind-up everything has in Season 3. I remember playing against enraged thor back when that first came out and it felt like I had to be super human to dodge his charge attack. The difficulty from Season 3 is artificial. If you don't have 10k+ defense the bosses weakest attack will 1-shot you. With a level 80 +8 2x rA enchant weapon it took me around 50 minutes to solo regina. I wouldn't say it was difficult though.
Luckily for me I had very good gear I could easily move over from other characters, so the stat increases don't really affect me after I did that. Though after playing gw2 and being able to swap top-level gear between characters for free I felt like I was getting scammed by having to spend $20 on unbinds to move over gear from 1 character to another.