CnC: Final War is a semi-total conversion for Red Alert 2: Yuri's Revenge that retells the Second Great War between Allied forces located mostly in Europe and the massive Soviet Empire, that has expanded well across the eastern continent.
The Legion Disciple is armed with a makeshift auto-rifle from previous wars, it's range and rate of fire lacking while it's stopping power is stronger. Disciples replace the Initiate as the Remnant Legion basic infantry.
Why they replaced some old Yuri units with the new ones for the Remnant Legion?
That was the plan from the start, I believe. Author just couldn't find some good sprites for alternative. Remnant Legion should be some kind of ragtag military formation from old times, it shouldn't have such psy capabilities.
If is not having a Psy capabilities for the Remnant Legion, why they still have a Mastermind unit.
EgoJisto is correct. Until I could finish removing the last ounces of Yuri units from the mod, I tried to at least lean on the flavor while I could. The Mastermind will eventually be updated to something else.