Sure I am aware of that, and clearly they have tested this plane in its ability to handle that. But the precise procedures for handling the condition would appear to vary from plane to plane, and it seems the role of a passenger pilot would reduce the operating range of the plane from "anything it can do" to "anything it would reasonably do". Clearly the imaginations of everyone involved didn't conceive of this scenario, and clearly the procedures required for the A320 are very different that require more than the standard certification training would cover.
It seems every time an Airbus crashes, it is the pilots fault, when it is clear the pilot has been doing certain things he was trained to do when encountering a scenario in all his previous experience. And frequently it's the case that's the wrong thing to do, or a misleading thing to do when flying an Airbus plane. For example pulling the circuit breaker, I'm told by a certified pilot is a reasonable action to take on many common planes. But is not procedure for an Airbus.
I guess where I'm going with this is that Airbus seems to require pilots to do differently things they have learned to do on other craft, possibly leading to their certification, and when confronted with a very rare but possibly survivable situation in Airbus, many do the wrong thing and crash. The deceased pilot is blamed (easy, cheap) but very little that seems like it is necessarily effective is done to fix what seems the actual problem: the plane is difficult to fly.