The 737’s airframe’s excellence is the reason Boeing was loath to let it go. It’s a really good airframe, and a market fit to boot for the transition from hub and spoke. A clean-sheet design for the 737 would look a lot like the 737. That is what makes the shortcuts tempting.
Engines, avionics and control software are distinct components and not part of the airframe. (Debatable only on engine cowlings and mounts. Neither of which were relevant to the 737 Max’s faults.)
You’re moving the goalposts because you didn’t understand what an airframe is.