Thats why I mix up their diet a little with Crickets, Silkworms, and Supers. Veriety is good. It would be like us eating the same thing every single day. It wouldn't be healthy. So to provide different nutrients in their diet they also get variety.
I am also not breeding leos though, I only have two so I can't say how it would affect reproduction and feeding many generations ecxlusively mealworms. Of course it wouldn't be healthy for the animals.