I had the same thing happen to my Pros, with one being much louder than the other and the noise cancelling barely working, and it turns out they just needed cleaning. A couple years of gunk and dust getting in the vents and speaker grill and one of them was noticeably worse than the other. After cleaning it turns out both were quite degraded and are now much better with fully functioning noise cancellation. Worth a try if they're otherwise good and you want to keep using them.
The Pros, on the other hand, in spite of me generally being quite careful with them (in contrast to the basic AirPods) had their noise canceling crap out at about the 2 year mark, and currently are slightly louder in one ear than the other (but the microphone still works, so they remain in service).
So, overall, I think I’ve had a similar experience to you with the Pros, but have been quite impressed with the non-Pro model.