Well no... but I base my evaluation on all his work. And if he suddenly, after a bunch of poor movies makes a decent one, I try to understand what makes it different. And saying that Christopher Nolan's contribution (with an impressive CV of movies like Memento, Insomnia, The Prestige, Inception and the Dark Knight Trilogy) IS making it different is not a bad analysis, I;d say.
Snyder: a bunch of sucky movies
Nolan: a bunch of great movies.
So if it's lousy, one could certainly question Nolan's producer qualities but not his directing skills. One could certainly doubt Snyder's abilities by then. If it's good, I can still make a case that Nolan's idea for Man of Steel (for it was his) and his producing skills contribute to its success.
Balance: Nolan makes the difference.