That makes sense. I had forgotten that the a7r did not have EFCS.
I went and looked at a bunch of other lenses on the a7r and a7r II. There was a consistent ~10 P-MPix difference in sharpness rating which would make sense if the EFCS is the issue.
sony 50 f/1.8 16 -> 26
sony 35 f/2.8 22 -> 32
sony 90 f/2.8 32 -> 42
sony 55 f/1.8 29 -> 40
sony 16-35 f/4 16 -> 26
sony 70-200 23 -> 35
sony 70-300 15 -> 24