Well whatever I said was based on articles like the one I posted it's by NASA ASRS. you can read it. B737 is made from B707 fuselage to use same dyes, casts etc. to save cost it has a low wing which helped that time for loading/unloading, Engine maintenance without ladder etc but it was misfit for high bypass bigger fan engine era. It's main problem. It had uncommanded rudder problem Boeing knew there's a problem but like MAX.only reacted after two fatal accidents in the US. Then why was STS required? I didn't find any in A300, A310 or B747. So there's an issue of instability at high pitch. Then continuous stretch from 100 series so to keep tail clearence takeoff and approach speeds are higher than say A320. To cater for high bypass bigger fan Engines hamster shaped intakes. Then it was not enough for max Engines. Boeing wanted to make a new aircaft but not to lose customers like SW and AA they launched Max and rest is history. Boeing had 757 perhaps they would have been better off modifying that. I have posted video of 737 max10 where on the takeoff run the main gear has to extend. So these are not exactly innovations but work arounds. Max has been severely criticized by people working on it as designed by monkeys and made by donkeys something like that. It's an aircraft to which only FAA certification may not be enough other authorities will do their own. It has threatened the credibility of both Boeing and FAA. I am not sure if it ever happened before.