As good a real life demonstration as you could wish of the proposition that if you take out 10% of the seats, per pax revenue will have to rise by 10% just to keep revenue the same - which broadly translates into an average fare rise of 10%.
Too simplistic.
If you take out 10% of the seats, you reduce the number of pax and also the weight of their baggage. This weight will be replaced by extremely lucrative cargo.
If you don't have the cargo, then less fuel is needed, thus reducing the weight still further.
My understanding is that Y pax provide the cost to run the flight and J pax are the major profit source - hence all the time and money spent on ground extras (lounges, check-in, etc) to attract and keep them