How does the Evaluation board rate a 1SG serving outside their MOS compared to their peers serving inside their MOS?

As you're likely aware, the Army changed from centralized enlisted promotion boards to selection boards last year. Since the primary results of the evaluation board are an OML, I assume the base concern you have is "will being a 1SG outside my MOS hurt my placement on the OML from the Evaluation Board?".

The senior officer and enlisted ranks are more about your leadership and planning capabilities than your technical knowledge.

While you were a junior/mid-grade NCO, the focus was more on you being expected to to know the 'what' and 'how' of your job (i.e., this is 'what' this does and this is 'how' it is used). At the senior levels, it's more of a focus on the planning ('when' and 'why'), resource allocation, and leadership of those who focus on the 'what' and 'how'.

While there might be some differences between the duties and responsibilities for a 1SG in your MOS field and those for a 1SG outside of your MOS, the commonalities between those two positions will be heavily focused on the senior traits (leadership, planning, and resource allocation) instead of the technical competencies of your MOS.

An evaluation board for an E-8 is going to focus more on those traits expected from a senior NCO instead of those of a junior/mid-grade one. Showing that you are able to excel at those traits is what's going to place you high on the OML.

It migh work out better for them to not work in their MOS. Especially If these skills are associated with complexities. Especially, if they are combat related. This might enhance the boards perception of that leader.

I’m retired now, but I truly believe that my 1SG time helped me to get a low board number. Plus, the leadership development of myself and my subordinates was valuable to all. My education and years in operations and staff, as well as my combat experience separated me from my peers as well as superior performance at MLC, and years of stellar evaluations. It takes a lot these days, but growth is the path to success.