As a curious follower of this thread, I'm 100% happy that the OP will get to travel in J. After all, that was the outcome that everyone was helping OP to receive.
That being said, I can't help but be a bit frustrated that this ultimately worked out exactly as AA hoped it would. That being something happens on an overbooked flight and seats opened up. It would have been a learning experience for each of us to understand what would have happened if those seats didn't open up. Specifically, OP arrives into PHL and is faced with a downgrade to Y or switch to the MAN flight. It just seems to me like booking in J and then getting little to no compensation outside of the miles back for travelling in Y would make anyone in this situation whole.