But Cap was smiling and joking in Endgame! So was Ant-Man. And both lost people they loved (or so they thought) in the previous Avengers movie. I distinctly remember them both quipping about Captain America's "ass" a LOT in that movie. And Clint was smiling and joking with Natasha when they went back to Vormir and this was AFTER his family disappeared in the Snap. The surviving Avengers seemed pretty chill about him murdering a bunch of dudes too. And let's not forget Korg "consoling" Thor after the destruction of Asgard: “The damage is not too bad. As long as the foundations are still strong, we can rebuild this place. It will become a haven for all peoples and aliens of the universe.” But just then, the ruins of Asgard explode and Korg adds, “Oof. Now, those foundations are gone. Sorry.” Thor seemed pretty chill about that too. So the MCU has set precedent by using levity to deal with trauma. Wanda's definitely using humor to deal with her emotional problems (Episode 7). Monica is not.