Regarding the engine certification I recall that the thrust on the engines had been increased but the full certification process had not been applied in this case with respect to that engine being in that a/c. Maybe I recall incorrectly but my basic point is that modern engines shouldnt lose blades and that this was part of the error chain. You could say another part of the chain was the mickey mouse vib guages fitted to the early B737-300s.
These are kind of softer issues somewhat subjective to one's opinion.
I've already commented on the reliability of things like vibration meters and smoke/fire detectors. We learn to live with them because without them we're even more in the dark.
I believe what you are getting at with the engine installation might be the normal course of growth/design changes within a certified installation and then walking into a new problem.
There is lots of room for argument on both sides. The certification doesn't really prove anything. It does a pretty good job of assessing relative safety. In spite of passing a few hundred test points during certification there are still numerous parts of the perceived acceptable envelope that are not tested until millions of flight hours. The CFM56 engine ran into this and so have lots of other engines. However, the certification of the installation anticipates this by designing tolerance to the blade loss event itself, for whatever reason.