"It has a lot of issues in my opinion", and, "it is complete shit, poorly written, ending objectively bad, blah blah blah" are two entirely different things. I can count the number of rational criticisms I've seen of DitF on one hand. The rest are mindless hate, and I dismiss that entirely.
I love the series, and I recognize that others do not. I respect other's opinions and I would never tell anyone what to like, but at the same time I'm so beyond sick and tired of the endless, mindless hate and vitriol that is directed at a perfectly fine series and story.
It isn't objectively bad. It is objectively a decent, unoriginal sci-fi plot with compelling romances and character stories. It has fantastic art, music, and animation. The pacing got weird towards the end. The narrative, while stumbling here and there, was strong overall. Those are facts, everything else is personal opinion.
The series is perfectly good as it is.
The manga is a nice little "what if" story.
That's it, period, the end.