I can agree to your point of it being a design failure - especially with two abilities in isolation only working a singular direction.
Brutal Slash, Butchery and Prescience have charges to allow you to pool up multiple casts for burst (at least on paper, tuning hasn’t always worked out that way).
The difference between these though are pretty sizeable. Similar to Warlock generating a secondary resource for a pool, Brutal Slash on Feral Druid is also developing Combo Points to do something else - they also have to manage 3? dots, to keep them busy enough to not run out of Brutal Slashes.
Prescience is an ability, designed to empower people - which you ideally want to empower them during Ebon Might/Cooldowns, so, even then, you may hold Prescience for a few moments just for it to align properly.
If we were to bring Warrior into this discussion as well, Raging Blow, similar to Feral Druid and Retribution as a mentioned prior, are busy enough of a specialization that you will not run out of Raging Blows.
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The case mentioned by you is that there are 3 “types” of charge systems, and how they are utilized. Butchery, unlike many other charge systems, works with 1 ability, and 1 ability only. You Butchery, Bomb off cooldown? Bomb. There are points in the rotation where you won’t want to Butchery, such as casting Death Charkram/Explosive Shot/Fury of the Eagle, or Coordinated Assault Kill Shot windows, but those cases only happen once every 45 seconds/2 minutes. As mentioned, you completely run out of gas after 35-40 seconds. That’s factoring in 10 seconds for the DC/ES/FotE window to come in, and then 5 seconds after FotE window is over. What does the specialization do for 20 seconds?
We already know the answer to this, because it happened in Season 1 - as that’s the tier set we are going back to. We Mongoose Bite/Raptor Striked on 5-10 targets and dropped on damage output tremendously.
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The only saving grace to those 20 seconds I would even think about as a remedy if nothing were to change is: Make Poison Injection remove on 2-3 targets at a time when you Mongoose/Raptor? That way you aren’t completely wasted on AoE and can at least do priority/small cleave.