Yea im more of the fan of how WoD handled our resources with Shadow Orbs in both it’s method of generation and how Devouring Plague consumed them.
Currently, we have many sources to build Insanity and because of that, we get a lot of little trickles of Insanity coming in which when you start out at zero insanity, it seems to take an unnecessary amount of time to build up to your first Devouring Plague.
However, once you are fully going and all your spells are going off and procing stuff, it is much easier to keep your insanity resources coming in and your able to constantly send out Devouring Plagues relatively quickly.
But back in WoD, your Devouring Plague cost 1-3 Shadow Orbs. So in theory you can toss out a Devouring Plague right after your initial Mind Blast. But typically you built up to 3 or more Shadow Orbs before you use Devouring Plague as each orb increase the damage it would do.
This allowed you to both build up Shadow Orbs and this spend them on Devouring Plague while also allowing Devouring Plague to hit hard since you could not just start spamming them out as you can do now with a full insanity bar and possible free Devouring Plague casts.
In short, you were able to chunk up your resources in fewer abilities instead of a lot of trickle in bite size amounts of resources as how Insanity works.
Because of WoD Shadow Orbs resource mechanic and ability to chunk up Shadow Orbs for Each Mind Blast, you were also able to generate Shadow Orbs with Shadow Word: Death. However Shadow Word: Death could only be used on targets at 20% health or less (if memory serves) and you were able to double tap SW:D with a glyph. This made your execution phase really strong because both SW:D would be hitting like a truck and it would also fuel your Shadow Orbs alongside Mind Blast which made you pump out Devouring Plagues like crazy.
So having said all that, I see both pros and cons of the way we managed and used our Shadow Orb resource vs Insanity resource but the main standout feature was that with Shadow Orbs, you could not spam Devouring Plague back to back multiple times with the Shadow Orbs system since we had a max of only 5 Shadow Orbs and Devouring Plague will consume all Shadow Orbs up to 3. So it kept Devouring Plague a hard hitting spell because its use was always limited in some manner.
Where as now, because you may be able to spam Devouring Plague back to back multiple times, they have to adjust its damage or it would essentially turn into a 1 shot button at times.
So I don’t know the best solution to make Devouring Plague scary again without it becoming overpowered.
But in terms of preferred resource system, I would take Shadow Orbs over Insanity every day of the week, no question.