Twins are fantastic until you want to cart a large load a long way . There is only one aeroplane on the market that can carry 520 pax and 10t of cargo over 7000nm or 500 pax over 7500nm . Can even do it from DXB in summer .
Now how many airlines need such a capability ? Not many. This is the same problem the 77X will have. The 773ER is an incredible aeroplane with performance that is right in the middle of the sweet spot for the majority of its operators . The cost of the new version for a capability that is not required by most operators will have a flow onto its sales. Good news for the 787 and 350 though. Not too many airlines seem keen to drop half a billion dollars on a depreciating asset. Be it a airbus or a John deer.