Rainboe
I agree with most of what you say, in that a RA failure in itself is a non event, especially as you do not even need a RA for CAT1.
However, you have to bear in mind that when it is coupled with the AT, the undetected errorneous information creates a more severe hazard.
However, again, this hazard should still not have been a catastrophic event, as I'm sure a FHA would verify.