I don't know. Last time I checked, Hollywood had not stopped making art films, historical biopics, literary adaptations, etc. Heck, this summer alone we've gotten biopics of Hank Williams, Miles Davis, and Nina Simone, and at the height of summer blockbuster season no less. And I'm looking forward to the upcoming movie adaptation of Girl on a Train.
And even on the genre front, there's no shortage of straight science fiction films, horror flicks, espionage thrillers, romantic comedies, kid's animated flicks, and so on.
It's quite true the above-mentioned types of movies are still being made, but only on a certain level. The most important factor in whether or not they get made is not who's making it or how good it is, but how cheaply it can be done. Only certain types of movies get decent budgets. Not only superhero movies, for sure, but we know the list: Effects- and action-heavy spectacles, romantic and bawdy comedies, horror movies and kids films of a certain "franchise" lineage, and sequels of successful movies.
I Saw the Light is a great example. Aside from the weak script, it looks like a small-scale TV movie. Lots of interiors, closeups, small crowds shot to make them look bigger. Compare that with 1976's
Bound for Glory about Woody Guthrie, which had extensive location shooting, whole blocks of a Depression-era town, miles of open road, farms and Hoovervilles, scenes shot atop moving trains and so on. I just can't imagine a musical biopic being given that kind of scale today.
An almost universally-acclaimed director, Paul Thomas Anderson, coming off a highly acclaimed and profitable movie,
There Will Be Blood, took five years to follow it up with
The Master and only got the deal when he secured some wealthy donor financing. Contrast that with Martin Scorsese coming off the commercial and critical success of
Taxi Driver: Almost immediately he was given basically a blank check to make whatever he wanted. Which was a stylistic musical that flopped.
Super hero films are a genre, and it is impossible to determine if a genre is played out until after the fact. For decades Western films dominated American cinema.... then one day they didn't.
In sheer numbers a
lot of Westerns were made in the '30s and '40s, but they were B-pictures, and by the mid '50s that business had moved to TV. I don't think there was ever a time when Westerns dominated A feature production, but I would be glad to be corrected if there are any figures on that.