@morrowmoriah I've had Welsh Harlequins, Indian Runners and Pekin's. In my experience, the Welshies have not laid consistently throughout the year. Not the worst (Indian Runner's) but surprisingly not the best (Pekin) either. However, I do not supplement their light, heat or feed during the autumn/winter months either (my girls free range year round in CA), so I don't know that doing so wouldn't help the situation. But I also don't mind having the seasonal break after the summer's bounty either.
Another theory I have could be genes. My Welshie girls are definitely not the Standard, their markings/coloring all differ greatly and one, the smallest, has a solid brown head with a bi-color beak and bight yellow feet! I know ducks have not been bred for egg production over the years, so I'm thinking my girls' obvious sub-par genetics could be one of the reason's they don't lay to the breed standard.