What makes most lawns look bad regarding sun is too little sun. Fescue and sunlight go together great.
Mulched leaves won't add that much, it takes more.
A good layer of at least 4" of topsoil is required at a minimum in order to maintain a nice lawn, 6" is even better. You also need to check the ph level as well. If the soil is acidic, you need to lime it to get a better balance suitable for the type of grass you want to grow.
Really good topsoil not only provides good organic matter, it retains moisture better as well. Clay will grow grass, you just have to water and fertilize a bunch. Really good topsoil smells, really smells as in organic material.
Get a good sample of your what your soil is and have it analyzed. It's not expensive and they can tell you what you need as far as ph and other minerals such as lime, nitrogen, etc . that you need.