Uniques are not all of the same rarity
When an item is generated rarity is determined first, it can be white, magic, rare or 1 of some number of unique rarity bands. exactly how many tiers of unique there are has not been publicly revealed.
If the item is unique, a unique is chosen from the chosen unique tier.If the item is not unique, then base type etc is determined.
In the case of chancing, base type never needs to be determined. however if a unique tier is chosen for which no unique of that base exists, then the item defaults down to a rare. So the existence of multiple uniques for a base only affects the probabilities of getting those uniques if more than 1 is on the same tier list.
So to be clear, in a world where infernal mantle did not exist, the chances of getting shavs would remain the same. All that would happen is you would get a rare on those rolls where you would have gotten infernal mantle.

Dec
Poe4orbs New Promotion, and this promotion
Gold to see you again. Poe4orbs appreciate that you had ordered on Path of Exile Currency on our site before.

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Eternal orbs still exist in standard
what we really need is to get rid of all the eternal orb influence in standard, or make a new dumpster league without eternals and eternalled mirror-able items destroying the market.

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poe4orbs:[Lake Of Kalandra] PoE 3.19 Templar Starter Builds
Here is the latest PoE 3.19 Templar League Starter | Fast | Endgame | Cheap Builds brought to you by PoECurrencyBuy.

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in Crucible, you'll learn about the ancient titans who once shaped the primordial surface of Wraeclast. If you're powerful enough, you will earn the ability to forge their power onto your weapons.

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Diablo III really has nothing on Path of Exile at this point other than graphics
As someone who loves Path of Exile. I would 100% agree Path Of Exile superior to Diablo 3 especially at the level you can play games like Starcraft and stuff.