"developed an annoying permanent yaw to the left, for which calibration has not worked to solve or alleviate"
I had exactly the same fault on my first Saitek X55. After some back and forth I got it replaced under warranty. A few months later that replacement had all the stick buttons stop working unless I twisted it 1/3 left or right. The initial attempt to solve that was a replacement stick handle (it's designed to be removed so you can change the re-centering spring, they supply 4 different ones). THAT handle had the same twist/rudder off-centre issue.
So they replaced the entire thing with an X56, which is mostly an X55 still, just a couple of new analogue thumbsticks replacing the old throttle mouse and one of the stick buttons (although that stick is also clickable as a button still).
I'm not confident, should I actually use it, that the X56 will have no issues before the 2 year warranty period is up.
In other words, I don't think Logitech can actually make the product quality worse.