To my knowledge there is nothing in AR 220-45 that covers this situation.
Duty Rosters are run by unit. Typically, you are correct a SSG(P) would be placed on the duty rosters with the SFC’s. If your unit is short on SSG’s it would be reasonable for you to continue to pull duty on the SSG duty roster.
If by chance there is not an exception as mentioned above then you might have room for a complaint.
The best course of action might be to speak with the individual responsible for the duty roster. Typically, the 1SG. In a professional manner discuss the issue with the 1SG and ask if they would share with you why you are still on the SSG roster.