Just my opinion Because I don't have a choice and keep mine on layer year round but over winter I mix 6 way grains into the layer. But if I could get mantience and mine weren't laying from fall on into winter this is what I would choose.
You know V your ducks better than me. My Muscovy always end laying once they have their big molt in early fall most of my Runners are over 8 yrs and most likely won’t pick up laying after although I thought molt was starting with them but not seeing much I am not sure with my youngest 1 yr to 5 yrs. It’s hit or miss. Just have to wait and see.
Ok, maybe I will mix the food for now. I have never had so many of my birds have an obvious molt in the fall. I guess most of them are 3 and under, so maybe as they get older the molt becomes more obvious and timed with the seasons.
My Runners and Buffs have what I call sneaky molt I rarely see many feathers and then one day I’ll look and see wing feathers growing in. It is so obvious with my goose and Muscovy. Yeah that would probably work mixing especially if there is oyster shell out in case they need an extra boost of calcium. I keep it out year round.