It’s making me wonder which what code is close enough to the patch’s changes that would affect brain burst damage. My guess is something to do with decoupling grenades and DoTs being able to trigger Slaughterer.
Warp Charge damage bonus and Brain Burst damage were buffed in February 2023:
Warp Unleashed was buffed (to also affect BB damage) in March 2023:
There have not been any buffs, nerfs or other changes regarding WC, BB or the WU feat since then. Right now, BB damage is the same as it was right after the March update.
Since the March update, BB can 2 shot Crushers on damnation.
This requires both BB to be cast at relatively high peril (for strong effect from Warp Unleashed), while the average number of active WC for the two BB casts must be ⋝ 5 (5+5, 4+6, 5+6 or 6+6).
The buff to Warp Unleashed also made it possible to 1 shot damnation Flamers with BB.
One option to 1 shot Flamers is to start casting BB at 0% peril while having 6 WC (peril gained from charging the BB grants just enough damage bonus from Warp Unleashed).
This only works at 6 WC, but not at 5 WC (+4% dmg per WC).
These specific breakpoints have existed since the March update, and they still work as of now (just tested them). They would no longer work, if the 10% buff from the February update was reverted (this is especially obvious and easy to reproduce for the one against Flamers, where you can start casting at exactly 0% Peril and which only works with 6 WC).
So the BB damage was not reduced back to pre buff values (at least not the damage against carapace and maniacs).
1st problem: The “bug” report makes the specific claim that BB damage was reverted to pre buff value, but provides no evidence or reasoning to validate the claim (which i guess makes sense, since the claim is false and can not be validated).
2nd problem: OP claims in a followup post, that the damage is about 15% lower than before, which does not match with the initial claim that the BB dmg buff was reverted, since BB damage was buffed by 10%, which would mean a 9% dmg decrease if the buff was reverted.
3rd problem: A bunch of people blindly believed it and started bashing FS for no reason.
OP probably unequipped Warp Unleashed, but does not know the effects of the feats they chose.