Why was ranged Devourer Nerfed?

A lot of ranged characters have "on hit apply stack" mechanics. Those have the potential to get really broken when you apply them 50% faster than normal.

Kayle was horrifying, yes, but the more egregious offenders were Vayne and the then-upcoming Kindred. Can you imagine doing an average of 23.25% current health on-hit? Because that's what Kindred would do with Sated Devourer, BotRK, and 6 stacks from the jungle.

Vayne and Twisted Fate were also very problematic with it. Kindred would also be another reason.

Mainly: It's less risky to do ranged attacks than it is to do melee attacks. Ranged was being more rewarded than melee.

Because now it's entirely possible for a ranged jungler to be successful if they are good at kiting. You couldn't do it before because the Jungle monster would time out if it couldn't hit you, but now that there's patience meters, that's not a problem. And since the only thing that was keeping devourer from being broken on ranged junglers like Vayne was the fact that they had to struggle through their clears because of the aggro system in place at the time, now that it's gone, it had to be nerfed for them.

Kindred, Vayne, Kayle

So far these comments are spot on.

having her passive doubled every other hit Procing her E in two hits

They nerfed it before kindred release because it would have been very good on them if they didn't.

Mainly because of ADCs Jungling. Mainly Vayne.