There is no such thing as a perfect process or a perfect system. And furthermore, expecting (or depending on) perfection is the wrong thing to do, because it is unrealistic.
In fact, during certification of (new) aircraft, there is an acknowledgement that some defects will remain.
Hence, defects such as these -- while should have been caught -- are not indicative of a process breakdown, certification breakdown, etc., but simply a reflection of reality.
The effects of any potential defect, however, should not be catastrophic. So what should be expected is a "graceful degradation" when failures do occur.
Actually a better analogy might be "defense in depth" used in security practice -- having multiple layers so that even a complete failure of one layer does not bring down the entire system.
The real question is then: even given a quadruple GCU failure taking down all four AC busses (due to this bug or some other malfunction) -- will that crash a 787?
Someone more familiar with 787s can correct me, but I think the answer is generally NO, as there is still the DC bus which will automatically run from batteries, before the ram air system kicking in (or possibly from APU as well.)