Ever since the whole Voidform became a thing and destroyed what Shadow was and capable of prior, the spec has been plagued with issues in every iteration.
In Legion, the spec only really did well in Raids and prolonged fights… or High level M+.
In PvP, they got gutted to be literally worthless… They got a PvP talent called Edge of Insanity that made it so you do a little more damage if you have max Insanity and you don’t go into Voidform anymore. Doing this forced you to not be able to use 3 abilities (Void Eruption, Void Bolt & Void Torrent) yet it was still a better option in PvP because you just get silenced or stunned or CC of anytime while in Voidform and it drains away forcing you to loose that window of damage regardless.
The entire idea around Voidform only works in a perfect situation where you are not moving, no external factors preventing you from casting and on a long fight that allows you to fully play out your rotation and them some.
- Doing world content caused you to nearly die if you tried pulling more then a few mobs.
- Doing PvP caused you to be a free kill target
- Doing any PvE content that forces you to move fast a lot (M+ / 5 mans) caused you to take forever to kill things compared to the rest of your group thus when you finally ramp up and getting started and popping off, they already killed everything which makes your DPS meter questionable as it appears you haven’t contributed… when is essence you really didn’t.
Then when it comes to scaling and balancing… it was an entire mess because when you were actually on long fights and able to free cast, you start scaling out of control which caused a balance nightmare cause the higher you scaled, the more the “base” DPS of the spec needed to be nerfed for “balance” which just made all the problems I listed even worse.
I cant tell you how awful the feeling was when my WoD Shadow Priest was able to decimate an entire raid of opposite faction of people easily with the tools I had prior to Voidform in Ashran. Then comes pre-patch and I cant kill a group of mobs questing without nearly dying. It was freaking sad and pathetic I just couldn’t handle it and moved on from the spec to play my Demon Hunter. The very sad part is that from the way past experiences went, when Pre-patch hit, you typically feel MORE powerful, not less.
Then in BFA it just became an even worse version and still had scaling issues which caused even more nerfs and causing more struggling in PvP and in any content when things die fast.
Shadowlands seemed like a step in the right direction in limiting the scaling potential from Voidform. But its still not an elegant spec and still had some scaling and balance issues.
If anything, the 10.0 talent trees need to figure out what it wants to do with the Void crap, push that to 1/2 of the tree and then use the other half to bring back WoD playstyles or even Wrath playstyle where we mainly focus on dots and Mind Flay, Mind Blast or both… which my version of the talent tree approach to 10.0 accomplishes all of the above and them some while still allowing you the freedom to pick other things that push you in the direction of…
- More Spirits play
- More Dots play
- More Mind Spells play
- More Void play
In conclusion, Voidform is a mess and I would argue a failed experiment when you compare it to WoD and the capability Shadow had at that time.
My Take on the Class and Shadow talent trees.