Better beware of notions like genius and inspiration; they are a sort of magic wand and should be used sparingly by anybody who wants to see things clearly.
God and Nature first made us what we are, and then out of our own created genius we make ourselves what we want to be. Follow always that great law. Let the sky and God be our limit and Eternity our measurement.
If a professional musician in a symphony orchestra is playing Beethoven. But this particular orchestra have played this particular chestnut so many times, they can play it in their sleep. Does the genius remain present in the music or not?
Anybody can put things together that belong together. to put things together that don't go together, and make it work, that takes genius like Mozart's. Yet he is presented in the play Amadeus as a kind of silly boy whom the gods loved.
The historian must have some conception of how men who are not historians behave. Otherwise he will move in a world of the dead. He can only gain that conception through personal experience, and he can only use his personal experiences when he is a genius.