Do you think a NCO should be able to keep his rank if he transitions to in a different branch in a different MOS.

Perhaps, a temporary reduction to see if the troop is worth their salt. If the command feels they are, they can be promoted. The other thing to consider is letting this soldier jump ahead in line of the juniors who have more experience in the field and time in that branch of service. It could be a bit of a disservice to them.

I have actually LIVED this question, I was an FC2 when I left the Navy and came in to the Army as a SPC. As much as it was painful to go through, and to have to take that pay cut, and set my career back as far as it did, there is some value to it. There is no way I had the technical knowledge to be an NCO in my field just transitioning over. NO WAY. I know some NCO's in my field that were "Fast Trackers" and all they care about is Rank or "Lickey/Chewey" schools, but don't know how to do their job, and not only do I but my peers look down on them. The Soldiers know they cannot go to them for any job related advice. So yeah, the reduction in rank is important. I don't believe that they would be ready to lead in their job. Just remember, the recruiters make it clear you are going to lose rank when you transition, so it is a voluntary thing, we that transitioned could have just re-upped and stayed in the same branch. So we knew what we were getting into!

This is a chain of command issue. If your leadership failed to check the individuals qualifications before arbitrarily placing them in charge of troops in situations that require specific expertise, then your chain has failed you completely.