Say you have a doff assignment you want to start. It's one of the friendly ones that starts with a 95% chance of success. The mission should ideally be performed (success) by a Gravimetric Scientist, but it will accept any science officer. Efficient and Logical are both (critical success) traits.
Now, you have a choice of two officers to put on the job. A purple quality gravimetric scientist who is efficient, or a purple quality photonic studies scientist who is both efficient and logical. Who do you pick?
Currently the photonic studies guy is the better choice for the assignment. Both officers will make the failure chance zero, but the photonic scientist's two critical success traits give a higher chance for a better outcome than the gravimetric scientist. Using the requested officer type leads to WORSE outcomes when you can reduce failure to zero such that the only factors which matter are the ones that increase the chance to critical.
As a fix, I propose that when a mission's Failure chance reaches zero, any further factors that would normally add Success (and whose contribution is wasted when there's no more Success possible) instead add Critical Success.
That way, when you actually have the correct officer called for by an assignment that has no failure rate, it will make sense to USE that correct officer.