I don’t know about zbrush, but I’m a storyboard artist and I need to draw a lot and draw quick and I found that a delay like that on Astropad was absolutely unusable.
Also, have you or anyone you know ever done any commercial art on an iPad? You can draw in procreate, sure, but how many art jobs are actually about drawing? You need specialized software for story boarding or designing or animation or any 3D work. I do agree Mac + Cintiq is a people’s favorite combo, though cost + performance are constantly the criticism of this setup. Disney and game studios might be able to afford that for their productions but not tv industry for example.
P.S. btw there are no pressure curves adjustments available right now on sidecar, but I assume 3rd party software could solve that potentially.