It is a good point, how the A321XLR compares to say the old Silverjet 767s when you have a density populated configuration vs I think it was just 96 premium customers.
I'm sure the wings on the A321 are more efficient & brakes for an aborted takeoff would be better but with better fuel burn would it require as much fuel as a 767 did?
I remember that Silverjet were to get x2 767ERs from TUI and were talking about Joberg, LA, Delhi & Shanghai before things went TU!