Shutter lag time only matters if 1) you are unfamiliar with your camera, or 2) you are using autofocus and the lag is unpredictable.
Lag is measured as instantaneous reaction to a stimulus. If you are comfortable with your camera, and you are anticipating movement in the viewfinder (rf or SLR), your finger is adding pressure as the decisive moment approaches. Lag isn't the factor any more - skill is. Unless you have an autofocus camera. Then at the decisive moment, <urp> no click! the damn camera didn't focus! Or you had it set to shutter priority, and <urp> no focus! the damn camera didn't focus!
Unless you don't know your camera. Then, the decisive moment approaches, and <urp> c'mon, click already!
I have RF, SLR, and GG cameras, and love 'em all. I do appreciate the quiet of an RF, especially in candid street photography. I love through the lens too. And then there's the ground glass. No one here has yet mentioned the wonder of the glass, under the dark cloth...