Should an officer/NCO be required to hold a leadership position prior to being a primary staff officer/NCO?

I think it is important to note that the two roles are fundamentally different. One is (primarily) about the Art of Command, while the other is all about the Science of Management (in support of Command).

This distinction drives the differences and also what makes someone good at one job vice the other. Quite simply, the staffer SHOULD be all about mission and metrics. Their JOB is to support their commander's intent and give him/her the information needed to make intelligent decisions. And then enforce those decision. They are not SUPPOSED to be exercising direct leadership in these roles. They are indirect roles by design and intent.

Direct leaders have a different purpose. They need to analyze the info they have and make the best decisions balancing the needs of the mission, the unit, and the people.

Different people do these jobs better or worse based on personality, training, temperament, knowledge, and seasoning. I advocate fitting Officers to the jobs they are best suited to, where they can make the best contribution to the overall organization.

I am fond of the British system, as explained to me, where an officer makes a selection several years into their career to either be a line or a staff specialist from there on in. I am also in favor of doing away with the lockstep up or out method we currently employ for officer retention. Quite simply, one can be a ROCKSTAR S3 or S4, who should NEVER lead troops.

However, to answer your actual question: I believe that before someone becomes an BC, they should have had significant staff experience. I believe that before someone becomes a primary staff Officer, they should have significant time with troops/units -though not necessarily as a commander. This is not for "leadership" per se. This is so they can translate what the charts in the books say to what will really happen as a result of the plans they write.

I think it should be a requirement, but not one with any strict enforcement.

Everyone should have the opportunity to lead troops before being put in a staff position, it is a central part of being an officer. As you continue your career, the opportunities become fewer and fewer to be in a command position so every effort should be made to put junior officers in this role. It broadens your experience and gives you additional perspectives on how things work.

All officers should serve in staff positions at some point, but that is pretty much a guarantee if they continue their career so the goal early on should be leadership and command.

As you know many try to avoid staff. In my branch we are pretty much guaranteed PL time. But as stated in other comments some are in a branch where they are destined for lengthy career in staff. I don't fault them but it would be preferred for all NCOs and Officers to have held a leadership position.

I think it is helpful, but not always possible, especially in the Reserve components. Some branches simply don't have the opportunity for leadership positions. For example, when I commissioned as a 2LT, I was a Chemical Officer in a state with no chemical units, and was assigned to a battalion staff. I later changed to Signal, and became the S-6 and Signal PL for the same battalion, but if I had stayed in my initial branch I probably would never have had any opportunity for leadership positions.

For a lot of branches (mine included), the career track starts you as a Battalion Staff Officer first (generally). It gives you the experience of working directly for a BN XO and a high-pressure environment where you get a bunch of additional duties. I found my time on staff to be a great learning experience and I took each task that I was assigned head on. It's probably different for every branch and situation, but for me it was a great progression from Battalion Staff to Company Executive Officer. 

The reason I said no is because an NCO is already a Leader of Soldiers. However; I feel that all Leaders and NCO's need to be a Staff Leader early in their career because it gives them time to grow. Lastly; I also think that their first line supervisor should shadow them along the way.

Having leadership time would greatly help NCOS and Officers while on staff. In my opinion too many staff officers and NCOs forget that they are their to support their subordinate units...not the other way around. For officers, having command time prior to assuming duties as a staff officer might help them better understand the relationship.

We once had an Officer Candidate who announced that he did not have any desire to be a Platoon Leader - he did not want to lead troops - he did not want to deal with Soldier issues. He was there because "A lieutenant makes more than a private". Said Officer Candidate did not make it through OCS and because of his contract...became a Specialist.

Officer/Warrant/NCO - we are all Leaders by the very virtue of our rank and position.

Now before they become a Staff Officer/NCO should they have held a Leadership position. In my book - absolutely.