It is true that students tend to respect a sea-returnee enlisted instructor more than a DIO. This is based on the simple fact that if someone has actually done something, they can teach it better than someone who has only studied how to do it. Operational experiance is how a majority of nukes actually learn how to be nukes. The theory is great. It's necessary for safe operation, but the first time you are on watch by yourself you will gain a wealth of operations knowlege. Concepts begin to make sense when you see how the plant actually reponds to various evolutions...
Before being dubbed Direct Input Officers, werent they Direct Input Limited Duty Officers?? 
First, the D.I.L.D.O. thing is an urban myth, fabricated out of whole cloth. The evidence of this is clear: almost every class from Mare Island to Orlando to Charleston has someone who claims to have been told by an officer (usually female) "I am a Direct Input Limited Duty Officer." Some of the stories have the officer actually spelling out the acronym. A sure sign of an urban myth is that lots and lots of people were witnesses to the same exact thing at different times and places with only minor changes to the details.
There is no such thing as a Direct Input Limited Duty Officer. DIO's and LDO's are too different creatures.
A Supply officer on board a sub is an LDO. An instructor at NPS is a Line Officer. That makes no sense at all, because the Porkchop will still be on a combatant ship while the teacher might be at risk for a paper cut. But, that's the way it is.
Second, I actually preferred the DIO's teaching me things like Math, Physics, Chemistry...etc. Even though they were not experienced sailors, they did have actual college degrees, often in the subjects they were teaching.
Third, the DIO's and the NUPOC's were not the same. DIO's were there to teach - period. Even though they still had the Admiral's interview, they were not the same as the officers who would eventually serve at sea. The NUPOC instructors were only asigned to teach (usually pre-NPS) until their classes formed. Some of them were actually drops awaiting orders.
