Why would GC imply patchwerk scenario when every interview he or another designer has done suggested that they do not like them and are moving away from anything that resembles one? We're simply at a point where the damage intake of a tank isn't enough to stress healer mana, period. That, plus the regularity and ease of healing stagger damage makes it basically irrelevant to tanking concerns. Let me illustrate with a crude picture:
I'm pretty sure people generally agree with the shape of the curves. Mastery specs, especially if you don't purify often, will take a higher amount overall damage (integrals of the curve), but their damage intake is smoother. Crit/haste builds dodge more and purify more stagger, but when hits connect a few times in a row their damage intake spikes much higher.
The red line is an imaginary EH point. If your damage intake rises to a point where it spikes past your EH ... well, you die. In this case, I've drawn it such that a mastery build doesn't die while a crit/haste build does. It's an arbitrary point, sure, but it's in the only location that matters - the EH bar could be well above both curves, in which case it's irrelevant what build you're going