While I like to bang on Boeing for being fucking dumb about 737MAX, the habit of copying an existing well-tested, approved design is something that should NOT be discouraged.
Re-use of existing validated solutions / components leads to faster development cycles and increased agility (financially) . This is achieved by making more critical components COTS (Commercial Off The Shelf - not one-off / custom) and re-usable as self-contained "modules" or "packages".
Reinventing the wheel for reinventing the wheel's sake is in most cases not a good use of resources.
That said, if the original design has issues, my above commentary is invalidated somewhat - you need to modify the design to fix the root cause, which should trigger a fresh round of validation and testing at the original specification levels or greater. And of course, you should always do fully integrated tests, even if all of the components were previously validated and approved. You pretty much always find stuff (maybe only in solution-integrated combination) - I believe that's what happened in this case.