I think you’re right. I have my machine upside down and the pulley/shaft looks to be spinning straight. But the glob of glue/epoxy on the shaft (of mine) makes it look terrible. I also printed some items out of PC FR and they all came out great with almost no z-banding.
I have the issue so far with PLA basic and PETG HF. Both use quite a bit of cooling. I think I found the issue with my dryed out PETG HF looking stringy. It is slowing down on outer layers to 60 mm per second with bambu studio and then can go as low as 10mm per second with a 50% overhang. This is a factory print setting that generated with Bambu PETG HF Grey. I was leaving and caught the print head going really really slow. I guess I accidently hit Balanced instead of Standard .20mm layer height. I actually think I just imported the file and chose the color and hit print.
