This will be a quick one.
QC4 items are currently very hard on the wrists since they require an unwieldy clicking rhythm to use, which limits their usage, even if they are well balanced in theory. Given that iframes are (to my knowledge) current capped at 1/4th of a second, giving all QC4 items QC5 would not change max dps output in the slightest, but it would greatly increase the usability of these items.
(also even if this makes witchbane and failnaught slightly better they already aren't great statwise relative to competition so I think that's fine)