you're cherry picking. There are a lot of movies that aren't "The Avengers" that somehow manage to be good, while not being humorless for the sake of being humorless. Is Spider Man 2 somehow a shitty movie because parker cracks jokes? Is Rises the better movie because everyone's wearing a frown?
And the shawarma scene is an odd bit of business to call out, since the scene was a totally silent scene of people eating food. It's funny to the audience because its exactly what would happen afterwards, but is rarely actually seen.. it's a humanizing moment.
And you're also way off in the treatment of "death and destruction", since the aftermath of the new york incident is explored at length with Tony having PTSD because of the whole thing in Iron Man 3 and Crime lords exploiting the rebuilding effort in Daredevil.
Banner is an international Fugitive in AoU after wrecking an african country in a brawl, and quits the avengers largely because of it. There was no coming back for the Hulk after that.
The Chaos from the sokolvia (sp?) incident itself is the entire point of Civil War. Jokes or not, all that mess had serious consequences.