The point of the 737max was that it was a brownfield design which wouldn't require recertification by airlines of all the pilots who are certified for 737min planes.

A 7B7 greenfield narrow body plane would probably have been faster to design and a better plane in lots of "don't lie to the pilot and fly into the ground when a sensor is busted" ways, but would have required all airlines to re-certify their pilots, which is both expensive and would have caused the airlines to consider airbus and boeing on the merits...