The MCU has rapists, crime lords, genocide, and plenty of horrible, ugly, no-good-rotten-scoundrels and many traumatic and often horrific deaths. I don't think Marvel really is in the habit of "constraining" their more hard-edge characters. If they're too intense for mainstream Avengers, they're more than happy to give them a spotlight on Netflix.
And the MCU films thrive on the director-touch Marvel selects. Avengers is so perfectly Whedon-esque, while Thor has many hallmarks of Kenneth Branaugh, Guardians of the Galaxy is pure James Gunn, and Joe Johnston was the perfect choice for Captain America: First Avenger, and Iron Man 3 is arguably the most Shane Black film Shane Black has ever made. Their fingerprints are all over these films.