Structural weaknesses and design defects in large commercial aircraft are nothing new, and are generally identified long before they cause an accident through a system of manufacturer testing, heavy maintenance checks and other in-service monitoring programs as has happened here. Also, this is nothing unique to Boeing, you will find similar issues cropping up from other makes and models of aircraft.
As an example, it took over 20 years for this issue to become apparent on the 737-classic
https://en.wikipedia.org/wiki/Boeing_737_rudder_issues
it then took over 4 years of investigation to nail down the cause beyond reasonable doubt and for the FAA to order replacement of the offending parts.