When I played WoW from 2008 - 2018, the Mik's Scrolling Battle Text would notify me of procs about 0.5 seconds before Power Aura or WeakAuras would notify me. What caused the delay in those addons, and how can I get a faster addons?
I'm guessing one addon listened for events in the combat log and the other one from UNIT_AURA event instead. From what I can recall, combat log events were faster than UNIT_AURA back when WoW still had something called spell batching (removed in Warlords of Draenor). Nowadays they should be the same.
For WeakAuras I think aura scans are throttled but there definitely shouldn't be as much as ~0.5s delay.