All very true. I know the Avengers for example was fun & action filled, basically a cartoon using real people. While DC movies on the other hand take a more grounded & serious tone.
Marvel tries to convey "morals" using fun, action and humor, in the movies.
And just as you said, the DC films are more grounded and serious. They try to convey not just morals, but the responsibility of the individual to act when injustice is done. Sitting there and doing nothing, is just the same as sitting there and watching a movie.
So, when you "watch" the movies from each, you come away with a different feeling from both.