Having almost all destro 40+ here are some thoughts to improve Balance / Gameplay
From the most relevant to the less :
Dok
Path of Dark Rites
-Soul Energy
This spell costs too much for what it does
It becomes useless in almost all situations (as it makes you run out of soul, even in full sov)
Few ideas to improve it :
Simply lower its ressources' requirement
Remove the 1.5 trigger as to chain cast for Khaine's Refreshment
Add more heal value to direct healings / extend it to all healings
-Transfusion Tactic
This tactic is too strong, making your hots over-powered
Maybe remove it, to explore more different builds
Path of Torture
-Drowning in Blood
Was more pleasant to play on a long CD, rather than to spam it
Replace the essence being blocked for an initial essence cost
-Wracking Agony
Remove the bonus speed and add a new spell
Would be best to get closer rdps/heal, instead of winning speed while already in the melee
Path of Sacrifice
Sould Ward and Blood of my Blood were great in some situations, it's a shame they got removed
Would be nice to make lifetap spells completely immune to healdebuffs again, or at least to improve their lifesteal value
Also, this spec could benefit from a group healing spell of other parties (maybe Devour Essence being apllied to many people?)
-Khaine's Encouragement
Change the bonus to a damage / lifetap one
-Khaine's Force
Reduce its cost to 60 Soul Essence
Sorcerer
Add a Heal Debuff spell / tactic
Marauder
Path of Brutality
Shame that it's the only spec not so worth to level max
-Unstable Convulsions Tactic
Improve it to Enchantment and Blessing
Add a vampiric value or a health bonus for every dispell
-Wave of Terror
Add an outgoing heal debuff
Shaman
-Dat Makes Me Dizzy Tactic
Since Gedup! got a boost :
add a bonus 10% x health to the tactic, proportionally to the cost of consuming ressources' points
Zealot
-Ritual Nexus
Improve a bit the range of them please
If the nexus could color swap with rituals, to old visuals, would be incredibly neat
Black Guard
-Feeding on Weakness
Improve the healing Value
Chosen
-Hastened Dismissal
Lower the height (and improve the lenght)
Squig Herder
-Sticky Squigz
Could either knocks back all the time, or make it unusable until enemy is at range
Choppa
Improve the dmg bonus of Berserk exhausting blows, as for now it's lower than Furious
Black Orc
-Changin' Da Plan
Change it for a toggle spell : when it's on, it would take 2/3 spells to change plan
(New to black orc, might be a terribly bad idea. Just found annoying to almost spam that spell on Cd)
Magus
Can now walk and summon daemonettes

Ps:
Mirrored class' spells should logically benefit quite the same of those changes
There is certainly other priorities, just hoping some ideas got your attention
On order I only have a rr60 WL for now, rest is ~cr25
I'd still like to complain about :
Archmage
Their dps build seems too strong on 1v1 (maybe it's the same for sham, didn't try yet)
Runepriest
-Immolating Grasp Tactic
25% proc is much, in 1v1 you get snared for the whole fight
White Lion
Their auto attack damage is too high
Perhaps lower it while improving their abilities' dps
-Trained to x
Could be nice to add a bonus to each one, at the cost of adding a long cd
For ex :
Threaten > More armor / resist
Also would be amazing to pick a unique skin for the lion, instead of adopting another cat everytime