The 2.5 patch brings some users a big input lag, by using a graphics API that’s infamous for causing problems in retail World of Warcraft.
I recall there being a “Reduce Input Lag” setting back then, but it is missing these days. Fortunately, under System -> Advanced tab, there is a “Graphics API” setting, and the “DirectX 11 Legacy” option removes the input lag, as well as other problems reported by the users of higher options.