They even have a talent where you can "Flee even when enemies are nearby" so the whole "Shoot, run, flee" is pretty much intended
Look at DOS1 Debuff potions, Enviroment talent, Weapon On hit effect. There are a lot of dead ends and underdeveloped stumps in released product. Talent allowing abuse missing AI for hunting is one of them.
I don't get what you're talking about that weapon on-hit effects didn't work (as you said in another thread). They work fine on regular attacks (at least in the EE).
Anyway stealth, snipe, and flee strat is pretty stupid, but if you want to play that way, whatever. But the fact that enemies don't search for you when you're stealthed and the only person in combat does feel just plain broken. It wouldn't even be that hard to script in some intelligent-ish behavior, and ought to be part of the AI 2.0.