So your argument is that, due to some freakish flaw in the RNG, certain base items will occur less frequently over time and that these happen to coincide with the base items that don't have a set/unique version associated with it.
Such an argument is completely illogical.
Even if we were to assume that certain base items grow less common over time due to a bad RNG, there's no reason why it would coincide with the items that have set/unique versions.
TC armo87 has these items: Sacred Armor, Colossus Girdle, Ogre Gauntlets, Myrmidon Boots, Corona, Diadem, Guardian Crown, Dream Spirit, Vortex Shield, Bloodlord Skull. For simplicity, let's examine only the first six items (since none of those are class-specific).
Sacred Armour has a set version and two unique versions.
Colossus Girdle has neither set version nor unique version.
Ogre Gauntlets has a unique version, but no set version.
Myrmiddon Greaves has a unique version, but no set version.
Corona has a set version and a unique version.
Diadem has a set version and a unique version.
So, by your argument, Colossus Girdle (and perhaps Ogre Gauntlets and Myrmiddon Greaves) could become more common than the other items, so that, over time, you end up with more HDRIs and HDMIs than originally, and that this is the cause for a decrease number of uniques and set items.
Why?
If we assume that certain items would become more common than others, it could be just as possible that, say, Sacred Armour and Corona are the more common ones, or any other combination of items. Why would it happen to pick exactly those items that result in more HDRIs and HDMIs?
Here, we just looked at part of a single TC. There are hundreds of different base items. If the items that become more common are decided arbitrarily (that is, without looking at what sets/uniques are available), the chances that the more common ones happen to be the ones without set/unique versions would be really, really small.
And this was all with the assumption that base items that should be equally likely really aren't and that there's a trend towards some being more common as time goes on. There isn't any such effect that I know of.
Really, it doesn't make any sense.
Such an argument is completely illogical.
Even if we were to assume that certain base items grow less common over time due to a bad RNG, there's no reason why it would coincide with the items that have set/unique versions.
TC armo87 has these items: Sacred Armor, Colossus Girdle, Ogre Gauntlets, Myrmidon Boots, Corona, Diadem, Guardian Crown, Dream Spirit, Vortex Shield, Bloodlord Skull. For simplicity, let's examine only the first six items (since none of those are class-specific).
Sacred Armour has a set version and two unique versions.
Colossus Girdle has neither set version nor unique version.
Ogre Gauntlets has a unique version, but no set version.
Myrmiddon Greaves has a unique version, but no set version.
Corona has a set version and a unique version.
Diadem has a set version and a unique version.
So, by your argument, Colossus Girdle (and perhaps Ogre Gauntlets and Myrmiddon Greaves) could become more common than the other items, so that, over time, you end up with more HDRIs and HDMIs than originally, and that this is the cause for a decrease number of uniques and set items.
Why?
If we assume that certain items would become more common than others, it could be just as possible that, say, Sacred Armour and Corona are the more common ones, or any other combination of items. Why would it happen to pick exactly those items that result in more HDRIs and HDMIs?
Here, we just looked at part of a single TC. There are hundreds of different base items. If the items that become more common are decided arbitrarily (that is, without looking at what sets/uniques are available), the chances that the more common ones happen to be the ones without set/unique versions would be really, really small.
And this was all with the assumption that base items that should be equally likely really aren't and that there's a trend towards some being more common as time goes on. There isn't any such effect that I know of.
Really, it doesn't make any sense.