So I was considering as Rashir is slowly one hitting everything or just a few hits and then bam the enemy is dead.

I was considering something so from levels 1-20, Play on Adept for me Adept was extremely hard, but now it's to easy

From 20-40, Play on the Higher Level after Adept

40+ Play on Master

What do you guys think? Does this help any?

If you really wanted to give yourself a challenge, I recommend starting with master.
But if it's too hard like that. I guess you could go slowly.

Adept is really that hard on 1-20? It feels to easy for me.

Works well for those who play first time. When more familiar, you could start with Expert and change to master near lvl 30

How do the higher difficultiy levels work? Do enemies just have more HP?

I think so, and you do less damage while they do more damage.

Probably playing a warrior. I play a lot of assassins and magic characters who don't do well in crowded battles. They do better when they either have crowd control or they are able to sneak kill. My mages, if they can control the crowd. My assassins, their stealth. So, yes adept is hard when you're squishy and don't wear a lot of armor.