Good review, I really like your analogy about the difference of DC v Marvel having more of a Black/White v Grey in character construct.

I have noticed this between Avenger's and X-Men also, not as pronounced but it show's the difference's between time's and generation's also.

You put a finger on what I couldn't find that let me down with the movie. It was made for a younger age group, I hadn't noticed this about Justice League but it was the same thing that put me off so many of the older comic movie's before Ironman. On that note go back and watch he first Avenger's and see how far the actor's skill's have come.