Sated Devourer, Rageblade and why the double-on-hit has no place in League

All I have is this simple argument: on-hits are not designed for it. And I'lll break down the two types to explain why neither is intended to be applied the way Rage/Sated allowed.

Item on-hits All damage amplifying on-hits are designed for a sustained fight. They aren't meant to change that to burst damage. Bork, Nashor's, and Wit's end all give enough damage to supplement a reasonably lengthy fight, but are not supposed to give enough to change that sustain damage into burst damage.

As an example, back when Bork was buffed and subsequently nerfed, it was too strong on Lucian in particular because of his ability to proc it for the increased lifesteal more often than the item is intended for without even needing to buy Rageblade.

Ability on-hits Champion abilities effected by Rage are likewise designed with a specific weakness in mind that is thrown out the window by the double on-hit. Third-hit passives, while they've become a bit of a meme, are probably the perfect number of hits to balance out such abilities. That's why we don't see passives that are every other hit or every fourth. 3 is just right. But with Rage active, such abilities activate every other attack instead of the intended every third, essentially removing the inherent timing balance given by the 3 hit requirement. This problem was rampant during Sated Devourer's reign, and has only been somewhat remedied by the fact Guinsoo's AP means it's a waste of around 550 gold if bought on many of the champions who abused Devourer.

Abilities with cooldowns linked to auto attacks have the same problem. Their cooldowns are adjusted to make it so that the attacker should be buying AS if they want them reduced, but become too short when they're reduced 50% more via the phantom hit. Yi's Q is the prime example of this, as it grants him invulnerability far more often than the ability is designed to give when you buy AS but not CDR.

And abilities that provide damage, similar to the items, like Yi's E and Udyr's Q, have the same issue as items. The most noteworthy example is Kai'sa's passive, which has both the issues present in damage and stacking since it has both functions.

Conclusion The Rage passive shortens the duration of a sustained fight far beyond what simply being fed would do. Which unbalances the function and intended drawbacks/weaknesses of every item and ability it interacts with. And while the fact it's AP has gated several champions from buying it due to cost, having champions that aren't able to abuse it doesn't justify allowing certain champions to do so.