Not quite like that, John.
If we take the "base" shot as the one that the camera's meter suggests was correctly exposed, then the highlights were hopelessly blown and there was no detail at all in the shadows. +4 EV was necessary to kill all the highlight clipping while -4 EV was required to reveal the shadow detail.
When you have the camera meter, you have no idea what "zone" of the scene it is setting as middle grey. You are therefore shooting blind. You have no idea if -4EV will capture the significant highlights...or be much too much. Same with +4EV on the low end. So your response on the number of stops need, overall, hold no basis of fact.
Your method could work if you analysed each RAW image in something like RAWdigger to see what EV it clipped at and where the lows where capyured. Unfortunately, if you have specular highlights or the sun, which you had no expectation in capturing and were going to let blow out, RAWdigger cannot distinguish between significant and insignificant.
You need to calibrate your camera to know the clipping point in RAW. I have found, on my 5D3, it is ~+3.5 stops, if I spot meter the brightest significant highlight. Once you have that, you can increase the EV until you see on the histogram that you have captured the darkest shadow. (I will actually overdo the shadows to ensure that I have add'l detail).
I find this method provide two possible benefits. First, it will maximize the DR captured, which often will allow one image to sufice....whereas the camera matrix/evaluative or centerweighted metering will often not. Second, it can allow you to minimize the number of shots required for blending/HDR.