Compared to the US, Japanese manga has much more variety in styles and stories, though some genres (flashy fighting, harem shit, Isekai shit) are beyond oversaturated.

I saw yesterday one guy talking about absolute Batman… another take on Batman as if we didn’t had enough. It could have the best writers and all but again, more Batman? The method Japan has is basically everyone gets a chance and try to standout with his idea by himself.
In US is get hired by one of the corpos that brought a successful idea and do something that sells.

The results are obvious there’s people that will buy Batman, Spiderman or Superman at every turn but for many there’s only so much Spandex superheroes you can have.