One thing I am curious is whether or not there is an unwritten rule at AA that when rebooking on non-OW airlines you are automatically downgraded to economy unless you make a fuss.

I have had three IROPs situations with AA and they were very quick to rebook on Air Canada twice on BA once. They had no problems getting me in business on BA

However when I was rebooked on Air Canada I was told they can only rebook economy despite my having a paid business class ticket, even if seats are available. I had to get a supervisor involved did get rebooked in business class as required by law but why couldn't the agents do it without my having to escalate.