The fact that this question continues to pop up again and again tells us right there that there is a problem.
We have an almost 18 year old game where only 2-3 encounters consistently drop artifacts. Everything else (Peerless & Champion Spawns) you have to kill 50 for a chance at a Legendary item. I'm not joking I could kill 50 Dreadhorn and have nothing to show for it...maybe not even a CC.
Gettin' a kick out of these "WTF do I gotta kill to get a decent item" threads.
I did 10 Lady Mel in Felucca last week trying to land some Legendary Woodland Armor. 10!! Junk....All of it!
There are some other MOBS dropping high end stuff, but I imagine it's a closely guarded secret. The danger is that as soon as it becomes public knowledge monster X,Y, Z are also dropping high end loot it gets nerfed. So players, understandably, don't advertise what is good and what isn't.