I just place a link to this old thread
here 1. Level scaling insures all items will have level requirements. This is bad because it railroads character progression and it feels contrived and gamey. They also can't stash high quality items (like Ankheg Plate) in the beginning of the game. They could, but it wouldn't matter.
Yeah D:OS is a game and one choice is no choice unless it does exclude other pathways. If you include drawbacks into your itemizations in order to reduce hard restrictions at all costs you will end up heavily relying on balance. (remember PoE). D:OS found a way how to (really situationally) turn itemization into a game that rewards smart play.

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).
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.
4. This clash between uniques and level scaled items destroys any kind of coherent itemization and plateau's item-based character progression. You just change the items you have with the "new model" every few levels. This is boring and misses the point of items. We aren't playing Barbie's Dress-up.
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?)
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"
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.
Crafting has the same problem. If you find enough items to reliably craft your gear it does not matter what you find. You just externate genericism from items onto ingredients and this then sticks back onto items. Baudolino's crafting system was really good (thread above as you know). It allows for multiple nearly independent ways of gear progression. I cannot imagine if it holds it's promises but they are good.
As a dedicated poker player I really liked that in order to maximise your gear, you could juggle around with them and predict which items you will most likely replace, so you can use as many skills+items+AP as possible.
It obviously does not work if you do not have any dire attribute needs. Then I can understand random loot is really dull.