Therefore, I can't help to wonder what makes these two variants different from the 737 NG or 747-8, both of which are based on older designs from the 60's/70's. Then of course you have the 777X...
I know the 767's 7-abreast seating and the 757's expensive production system have come up before, but is there anything else that made the 757 and 767's heydays so short-lived compared to other aged aircraft families (737, A320CEO, A330, 777, etc...).
Please don't take this as another 757 MAX thread - I simply want to know what made these families different from their Boeing and Airbus contemporaries
