Im sorry I missed the bit about dietary restrictions.

cupcakes and muffins have similar sugar contents, are both made with identical procedures and ratios of ingredients. That is why they are the same. Cupcakes are cake batter poured into a different sized baking tin.

And Im saying by removing sugar you are going to change the consistency of the product significantly. All that sugar isn’t there just for taste as sugar also retains moisture in baked goods. There are always negative consequences to “just removing sugar” and you will be better off finding a recipe that was formulated to have less sugar.