Also keep in mind its more the "artists process" that justifies the tool. As Erik pointed out a number of great key importances, although his reasons we can leave aside for taking the A7R2 as a preferred tool for his image making, but Erik is a super critical guy when it comes to IQ, and maybe I'd ask him to refocus some past tests shots he has taken, but certainly it should give you a hint to how close the IQ gap has come between the platforms.
Viewfinder, lens characteristics, and color aside, when you are making images, and not taking them, sure the meat of the MF file is "thicker" and you can feel how it takes more effort before things start cracking, but you really aren't always at the limits of things when you work in a methodical, or even not so methodical approach with some of the cameras and their DR and such.
But I must say, with a AA filter that makes images milky and fuzzy, there is some step in clarity that people claim can be had with some sharpening and such, but you really don't get that 3D effect, maybe less difference with a shallow DOF, but there is a quality, even discussed here at least a couple other times in depth.
So I don't know how the Canon "negates" the AA effect, but the Sony doesn't have it, nor the Olympus.
Some test showing the oly with multishot being even clearer than some other camera I forgot it was up against, maybe the Nik810, but it had the edge for THAT particular setup of usage....
So those are very good tools for IQ. But say your an journalist/event/Corp shooter by day (75% of your work) and Stills or Fine artist by night and you want the right tool. I wouldn't put all my eggs into a A7r2 body to withstand the beatings I give it in the field. Years back I would have a 1Ds body, and a prosumer Canon body as backup. I do the backup from time to time, but with a A7r2, I would surely need to have 2 bodies, and bunch of batteries from what I hear.
Anyway, you are correct that you really DON'T need it, as much as you need a Ferrari to get to work faster in the mornings.