This is a Gletscherbruch Test of my original Sony FE70-300G.

Basically I shot a real world image from 600 feet away and then, while keeping the exact same focus and exposure, shifted the central subject into the 4 far corner quadrants by re-aligning that subject via the tripod positioning.

I have composited (at 100%) that center selection from the appropriate section of each re-aligned image. In this case I started in the center, shot the 4 corner positions and then re-shot the center to verify initial focus.
The first shot is actually the white outlined insert and the one outlined in red was last.
I used the same sharpening and levels on all segments and each one was processed in ACR using the appropriate lens profile. That way the modest vignetting is minimized.

My original lens didn’t fare too well. The center is great, as is the far upper left corner…given that it is a corner and wide open. The lower right and left are weaker and the upper right the decidedly weakest. The 4 corners should be the exact same.
I can’t really perceive this field tilt in a single garden variety shot so far but this is exactly the same results I received from my indoor test charts from 34 feet away.

Ultimately the lens was replaced by a significantly better lens.