First things first, my weight really is close to 100 kg so no offense taken nor appropriate
Your reasoning makes sense, a duck's body does a lot of work daily and needs lots of input for that.
As I work mostly with code and numbers my "something doesn't work out" detector triggered though at the calculation of protein needed daily.
Think about protein content of complete layer feed - it's typically around 16%, and the normal daily consumption is around 150 g. That works out to 24 g of protein. So what's "the norm" would actually be a severe lack of protein compared to the egg calculation.
The thing is that an egg is not close to entirely protein; there's a lot of water. Most of the weight is water. An egg's protein content is, if I understand correctly, around 15%.
This is very close to the layer feed percentage. We could roughly say that when a ducks eats 150 g of feed, half of that is spent on the daily egg and the other half is for the duck's "private purposes" which definitely exist as the body is regenerated constantly.
But your point stands: a duck does a LOT of work to produce eggs. Hats off to our ducks. And if it's to happen every day, it also requires a LOT of proper food.
Speaking of which, it is now close to 7:30 and the ducks which have been quacking for the last hour to be let out of the coop have fallen silent... from my very limited experience this possibly means there's another egg. Or it's another thing completely. Let's go and find out.