It's a fine line for BW, and I don't envy the devs who are in a tricky aituation. If they increase the unique item drop rate too much, and stop with the useless duplicates of uniques, then manifests would fill too quickly, and we would lose the sense of progression, and there isn't much else in DAMP other than promotion grinding.
If, on the other hand, they continue to let RNGeezus troll the cr*p out of players, they won't feel that there's any sense of progression.
Here`s the thing - I am already at the "isn`t much else in DAMP other than promotion grinding", and I`ve been there from about 500k into the game. That was roughly the time where I have gotten 2nd best bow and about the top 4 staves, plus 2nd best shield and some other useful stuff, including TWIN Wicked Grace. I suspect that anybody at around 500k mark has useful stuff, varying anywhere from 4th best in slot to 1st or 2nd. By the MAX or 1 mil we are already at the "I am missing only one, two or a max of five top items to have full best in slot all toons".
So, by 500k or so, this game is done regardless, and you`re going into "oh look! let`s grind promotions!". So, yes, by let`s say 1 mil, we SHOULD have everything, because at that time is doing more harm than good - you are either the type of player that doesn`t give a damn, or you`re getting pissed off about the lack of ... entitlement and moving on to other games that are more logical into their progression, and not dice oriented.