If there were 15 open seats, why do you assume that you would have been seated in a middle J seat?
In my humble opinion, the Worst J seat beats the best Y seat.
To address your gripe, each program has its relative weaknesses. AA´s is its ``expediate fees``. Conversely, UA fliers suffer with a $75- unused award redeposit fee.
And if you were a CO flier, then you would not even have the option to pay $75 same day.