I’ll start with, there is an Official response from a Blizzard QA lead on this matter already, saying its working as intended by the Reference Client of 1.12.0. But as we’ve seen with the C’thun,Blade of Eternal Darkness and Frost wand changes that the reference client doesn’t always reflect the final version of WoW Vanilla.
Now There is just one simple line of text from the 1.12.1 patch note “Fixed an issue where weapon procs will now work with instant abilities.” which could be associated with why people are complaining about the lower proc rates.
This line isn’t elaborated on, but what if it was just a simple fix that makes weapon procs ignore GCD. This would stop people from having to figure out what spells/abilities do and don’t stop weapon procs; as QA lead Aggrend said “no, we are not going to post a full list of which spells are in which spell school or defense categories”
Thank you for coming to my terrible Ted Talk about even if this is a Feature and not a bug, it sure as hell feels like a bug from the User side.
Previous threads on this topic Proc Weapons and the GCD and Hamstring Reduces the Proc Rate of Nightfall in 2020