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Your last sentence is one way out of your #2 and #3. Let uniques be like collectibles/sets that you will find on the course of the game and you can unlock their power at the end of the game/when you have all of them (+ some generous requirements).
I suppose, but they wouldn't have the bite of the Ankheg Plate :p
Also #3 is a false dichotomy. If you were to find a unique early game it is either overpowered or doomed to be replaced. Or it dooms the rest of the game to have loot of no better quality - which clashes with game progression, obviously.
How is it a false dichotomy though? If uniques scale, then it punishes you for getting them early. There is no way around that if they scale. There is nothing wrong with not having any items more powerful than this. Like I said, we don't need to change items constantly to feel progression.
You are basically saying that every item within the game should be unique if you even consider equipping them. Everything else is a placeholder for gold.
Or do you say the opposite? At least you exclude any inbetween. (Isn't how the strength of items is distributed independent of the system?)
Yes, I suppose. Though "unique" isn't the right word. Not-random is a better one. DA:O did this well I feel.
ToB made everything very unique and their item description went from 1.5-2.x pages to 5 lines for each item.
"Whoever invented the Ring of the Ram invented this godly Staff+6"
ToB threw epics at you, though. That is one of the design flaws of high level D&D.
A truly unique item is not primarily stronger than other loot. It is unique up to a point you did not expect it to be in the game. You did not expect that you would even want it. Surprise your audience, which you cannot do after strongly grounded intervals. Lilarcor won't do it ...again.
That is true, but it concerns the lore and surprise factor of the items rather than the mechanics of them.
Then I can understand random loot is really dull.
That is the one of the main points (that I forgot to mention), that random loot is boring.
The thread you linked is mostly directed at crafting, though. It didn't concern itself with the overall mechanics of random vs unique items.