Sure, it is possible the Legion series could be good. Stranger things have happened. I'll probably watch the pilot.
But it has a massive hurdle to overcome, and one that no series that I know of has managed. To take God, angels, demons, Lucifer whoever, and make an interesting story of it without making it an expressly religious tale.
From most reports(haven't seen it myself) Supernatural took a dip in quality when it introduced God and all that stuff.
The Golden Compass books started great and faded fast as God and the war became the main plot of things.
The Prophecy movies? The Left Behind movies? Laughable.
The only time Angels/God/etc elements seem to work well that I can recall is lighter stuff like A Wonderful Life or Touched By an Angel.
And Legion is not going to be anything like those in tone.