Even normal non-boss npcs while on a stealth assassination mission with zero stealth gears?
Yes, a stealth assasination mission you are supposed to dodge the regular mobs and kill the boss. The boss is weak, while the rest of the enemies are strong. It tells you this in the description of the mission before you start it.
Hmm Now I have a question; Where do I go on the AVWW wiki to find out what each stats on gear does?
The wiki doesn't have much, because in-game there is pretty much everything there. I believe it tells you this directly in the encyclopedia, or in the case of equipment mainly it would tell you in the tooltips.
I killed that boss in several shots so not much of "stealth" feeling to it >D. To be fair although that boss was level 1 with vulnerable to light spell and I had level 2 light spell.
Once you reach the boss, you've basically won: it's a stealth mission to reach him in the first place, with pumped-up monsters all the way through until you reach him, and he's about 10x weaker than usual. Again noted in the mission description.