I know that's a popular belief but the post cat O2 sensors can effect fueling by 10% found in 98-00 Vortec disassembly. Haven't found it yet in LS stuff.. but in a 0411 PCM vehicle I did have one bad cat that threw off same bank fueling and when the post cat O2 were disabled it went away. So I'm guessing the same scenario. The bank with faulty cat post O2 sensor voltage was swinging like a pre cat O2.

You do need to physically disconnect post cat to disable them. Turning off DTC does not disable them. I usually fix them discretely and leave them all plugged in.

I didn't study your data log hard but looked like the big fueling issues were at idle and low RPM. I'd be very curious if you still had post cat O2 hooked up during that log and seeing another log with them disconnected with no other changes!