Well, it could also be argued that Apocalypse was mind controlling Magneto and he was not responsible for his actions. But, even if you don't buy that, I would counter with the following...
You stated that MOS was in line with Superman of the comics. I disagree entirely. His actions in the movie were opposite those of comic book Superman (as I described above). Meanwhile, Magneto having no regard for human life is extremely consistent with Magneto of the comic books.
To expand our debate a bit further, I feel that most Marvel movies (including the X-men franchise which is not produced by Marvel Entertainment) provide the viewer with a great mix of action and light-hearted/comedic moments. Conversely, the DC movies tend to go in more of a dark, foreboding, apocalyptic direction. I don't read current comics, but when I did, I felt the opposite was true. DC comics were brighter and less dour. They took place in imaginary cities and were less realistic. Marvel comics were a bit darker, with more death and destruction and more of an attempt to make you think that they were depicting realistic events.
For whatever reason, the 2 companies have flip flopped with their movie making. Except, I feel that Marvel depicts a world similar to the one we live in, but with beings that have super powers, while DC depicts more of an apocalyptic dark world where the existence of super powered being results in a worse outcome than the world we currently live in. I guess that might be the overall issue I have with DC movies. I feel that the world should be displayed as a better place with the addition of super heroes, not a darker place where humans have to live in more fear that they are going to get caught in the crossfire between warring super beings.