^I didn't realize he tried to write a Superman movie. Make me wonder if this isn't just frustration speaking.
As for what he actually says, I have to disagree. I don't see where any of the DC characters abilities are really that much worse than the Marvel characters. Hell, one of the next movies has a talking raccoon and a sentient tree among it's cast members. We've gotten plenty of adaptations over the last few years that have shown that the characters still work fine today. I know they've been mostly animated, but I think the things he says were true, then no versions of the characters would be popular today.
The difficulty in writing DC characters is not that they're too goofy, but that they're too strong.
Superman's power is to do anything that the plot requires, essentially. Writer are fond of pulling new powers out of their assess. But even if you limit him to the basics of flight super-speed, super-strength, and invulnerability, you can't challenge him. Even the Richerd Donnor movies required that he be a dumbass in order to provide a suitable challenge.
Green Lantern can literally do anything, limited only by his willpower and imagination. Creating a villain to fight that is not easy, as we saw.
The Flash's abilities actually make him more powerful than Superman. While he lacks flight, he's capable of running at lightspeed, producing infinite energy. Punching someone at full speed would release enough energy to destroy the earth several times over. With the exception of the several evil Flashes, there's nothing that can stand against him even before you get his weird speed-manipulating powers into it.
Wonder Woman is generally depicted as Superman with boobs these days and faces the same problems.
And the Martian Manhunter is Superman with shapeshifting and telepathy, which makes him even worse.