Most of the lags on Macs are relative to that, now Mac users must have resolution same as monitor (not a 5k/2 for example) and render 5k textures.
If you choose scaling in wow game setting to 50% (like it was), graphics become blurry and looks bad
Before 8.3 there was a computed scaling resolution for retina monitors, now Mac users with retina must render x2 textures instead of scaling it programmaticaly.
Blizzard, please, restore that ability, and most of mac issues will gone away
So, if we have 5k resolution and 5k resolution scaling, on my imac, my fans become crazy and GPU usage (Radeon pro 8GB) is 100% and heating up
I think now GPU renders most part of graphics without CPU usage, but Macs doesnt have as good videocards as windows PCs, so just rever this change in client, because all lags are from that change