The movie has myriad problems, but "being dark" isn't one of them. At all. It may not be my personal tonal preference, but if a movie has good characters and competent storytelling, it can be a successful "dark" comic book movie.

The problems for this movie rest entirely upon the storytelling, the characters, and Snyder's seeming indifference toward consistent character behavior. (Also giving the women less than nothing to do doesn't help at all.)

So yeah, I agree that DC can make a "dark" universe that works... but they have to get Snyder out of there.

Of course, now all anyone is saying from the WB camp is that Suicide Squad is being reshot to add more jokes, James Wan keeps mentioning how "fun" Aquaman is going to be, and the WB people keep putting out in the press that Justice League will be non-stop kinetic action stuff... so they may just be learning the wrong lesson. I'm all for levity, but if they focus on "fun" without fixing the storytelling, shit won't change one bit.