I would call DGM dark version of FMA that continued something that FMA lost at some point of story. Like...thing is if you try replace Allen in this story with Edward, I'm curious how soon enough he will lose his mind. Problem is that story is so deep, that you can't just talk with villain, or suppose to be villain character, and made him turn good. Like people here did really horrible things from human experiments to killing nations, whole countries. But what's important that they have real reasons to do what they are doing. And solution that could easily save world didn't exist at all.
In best case scenario DGM will end with reset world to the part when there will exist only two human being, new Adam and Eve that will start everything from the begining.
So yeah, if FMA as some point lose part of detective story, DGM went instead deeper in it.
So even if DGM was a bit similar to FMA, it overed at first few chapters?! At least that my take