If you have the means to do so (a large enough mash tun), you could skip the sparge all together. I have really come to like going this route the last couple years. Not that sparging is hard at all, this just saves even more time, energy and effort.
I think the basis of your question is why are there common standards of 1.25-1.5 qts per lb of grain for mashing. Why is the mash split like it is? I think it just comes down to having a good balance of water to mash with and then water to sparge with, but depends on the grain bill, batch size...etc. You can disregard that and do whatever you want with your volumes, the idea of the water ratios again is to get baseline for repeatability in your process and for many brewers a way to maximize efficiency by rinsing (sparging) the grains after the mash.
If you are jumping into all grain, I would seriously look into BIAB "style" brewing, doesn't have to be in a bag per say...look at full volume, no sparge brewing if it interests you. The only thing to lose is a bit of efficiency, but depending on what your setup is it's not that big of a loss or added cost for most brewers. I re-circulate the mash the entire time and with full volume, no sparge mashing I average 75% which was what I was getting doing batch sparge before my RoboBrew re-circulating setup.