I have never seen anyone complain seriously about TDK trilogy being too dark. (Which isn't apart of the DCEU, but whatever).
When people complain the DCEU is too grim/dark it's not because they don't like grim/dark or don't think it's good. It's because characters like SUPERMAN aren't grim/dark. Logan is a grim/dark character. Daredevil is a grim/dark character. Superman is a man who flies around in bright blue and red who is an embodiment of hope, not an emo "woe is me, why do I have to save people" type character.
And I'm really hating this idea that people keep trying to push out the idea that MCU invented action movies with quips in them. But when people complain it isn't funny, that isn't a problem with the humor, it's a problem with the QUALITY. Back onto TDK trilogy, Daredevil and Logan, they weren't humorless. They were dark, they were grim, they could be depressing as all hell, but they weren't humorless.
And of course you don't buy there isn't a bias against DC. No way is it possible for people to not like a movie that much. Especially people who claim to actually be fans of the comics or characters. Can't at all be people don't like Snyder just deciding to shoot Jimmy Olsen in the head because he didn't know what else to do with him. Or turning Pa Kent into the exact opposite kind of character he is. Or pissed that Batman is completely fine just mowing down badguys with guns. Totally not a bias AGAINST DC that people don't like these things.