BUT...the tool indexes off the base.
I here what you're saying grabbing the rim to seat the primer. However, if doesn't matter because I still measure for seating depth, 0.002-0.003 below flush, using my calipers which measure off the base.
I understand the cases are dynamic and changing to some degree with every firing. The brass is flowing etc. BUT..it makes me feel better knowing at least from the baseline my cases are consistent. I shoot < 500 yards but I always strive for good reloads in hopes to make clean/fast harvest.
Realistically, if I took the time to find out which pieces of brass shoots best, it would be time well spent!! Shoot the brass, if shoots good, put it in the good lot. If still shoots good 2nd time around keep them in the good lot. Etc. If brass shoots bad, goes in the bad lot, shoot 2nd time if still bad, be done with it. If shoots good keep it in the bad > good lot. If shoots good a 3rd time likely good brass but poor first shot. If it shoots bad, now 2/3 bad, if goes in the bad lot permanently. I probably end up with a dam good lot of brass regardless of brass specs. Truth be told I don't have the time.
Point is some brass shoots well but it's not always clear why. Some brass may have near perfect specs but be inconsistent. Other brass have have subpar specs but consistently shoots well.
It's the rabbit hole of reloading. You think you figured it out then you realize you haven't. HaHa!