A good editor tells creators that if they want to make something new it must be original not making a copy. A copy will always be a copy.
Messing with characters who have been around for decades it is not a wise thing to do. You had readers invest in these characters for years and suddenly you expect that after all the time, money and passion they have given, that gets thrown under a bus? for a copy?
If they want to create a new superhero by all means, problem is, can they come up with something that gains attention? something new or borrowing from someone's else idea? Or the brand Superman, Batman etc is a shortcut?
American comics have always been influenced by the current tendencies by or large, now American comics need to compete in the USA itself with manga. Which has overtaken superhero comics. Why manga has achieved this cannot be rounded up in a thread. Nor the usual conclusions given in the US why this happened, such as manga have a start and an end. There are mangas that have been ongoing for many years. Manga attract people across the globe irrespective of the cultural divides etc.
In Europe you will find more people who grew up with japanese anime and manga than Superheroes, not just europeans mind it, Go Nagai's creations for example have lots of fans even in the arab world. Although superhero movies have done extremely well and popular, they don't translate in any boost to comic sales.
issue is can American comics do what manga did and appeal beyond the borders of the USA with older characters and legacy ones? My opinion is the decline is irreversible.