Am I Under-Leveled?

I’m in Act II on Expeditioner difficulty. My average level is 26.

I just reached Mask Island and got the three path choices. The two optional paths? They absolutely one-shot me. No chance. The main path boss I can handle his phase one. I can parry everything, but it takes me like 10–12 minutes just to get through it. Then his phase two comes in, and it’s hell. I get almost one shot I can't even move or dodge or parry

I tried farming XP in the arena. It gives me 26k XP and every fight takes 3–5 mins, but I need like 60–70k per level now, i went from 23 to 26 and it’s becoming boring.

Also I’ve seen posts of people already reaching level 50–70 i mean the game is only been out for like 3 days How they leveling that fast