the difference is that if you sit on 4 embers, you'll potentially lose some of them. Sure normally you wouldnt, just like no class would. but if ya need the max burst, then you need to stall = dps loss. Destro locks just lose less dps from it (but more from having no procs with them)
I cant think of any class that has the option you want moonkins to have. Every class can stall their burst, none will get that burst to be greater than their normal rotation burst by stalling it.
I never said the two resources would be the same. Rage/energy are the equivalent of mana.
Moonkins need to stall eclipse and starfall for max on demand damage.
Warriors need to stall abilities, such as colossus smash, for max on demand damage
Rogues need to stall combo points for max on demand damage
Monks need to stall tigereye brew and chi for max on demand damage
Priests need to stall shadow orbs for max on demand damage
and the list continues with every class.
Stalling will always be a dps loss, some classes can do it "better" but lose dps by not having procs etc for it (eg. destro locks usually burst all embers when procs are up, when they do this without them, its a dps)
I fail to see how shadow priests have that mechanic. Not using DP with 3 shadow orbs is a major dps loss, Warlocks have it "better" but even they have a downside to that gameplay which i already explained - and its pretty major.