Regarding Set Mechanics:
The vast majority of naturally dropped set items are only used for leveling. Usually, when an endgame build wants to benefit from a set, it does so by transforming a powerful exalted item into its set equivalent. As a result, naturally dropped set items tend to become obsolete in the endgame and end up serving mostly as crafting materials.
Regarding the Corruption Mechanic:
Although corruption can provide some interesting effects, using it on a carefully crafted endgame item is generally impractical because of the potential drawbacks. This is understandable, since corruption can turn an already powerful item into something extremely powerful, but it also means that Corruption Runes are often underutilized.
How Corruption Works on Set Items:
In most cases, corrupting a set item transforms it into a random exalted item of the same type, inheriting a random roll from the set item’s affixes. Sometimes the original set item is preserved, with its rolls being maximized or minimized. Other times, the item simply becomes unusable. Currently, there is no outcome where a set item is retained while gaining only a corruption prefix or suffix - At least in the tests I’ve done. If there’s already a chance of that happening, then you can ignore the post..
Potential Improvement:
If corrupting a naturally dropped set item had a chance to grant one of the special corruption effects, it could make set items competitive endgame options. For example, a corrupted Abandoned Eyes of the Weaver with +1 to Skill Level, or a corrupted Sunforged Hammer with the Forged Weapons on Hit effect.
Exalted items transformed into corrupted set items with these same effects would still be stronger, but they are significantly more difficult to craft. A naturally dropped set item would be much easier to obtain and improve, since all you need to do is farm the item and use Corruption Runes on it repeatedly.
This would increase the utility and, consequently, the value of set items. Since set items are currently very easy to obtain, increasing their rarity could be one way to help balance such a system.