The super hero genre is an individualist power fantasy. It's about giving power to individuals, whereas in real life power rests in groups and systems. That includes the power to effect social change.
It's an escapist response to living in an impossibly complicated world where we want to do good, but we feel powerless and unable to.
The story of a character organizing a series of protests wouldn't really benefit from that character having super powers. Using super powers (physical force) to push political beliefs is terrorism.
So the constraints of the genre mean that social messages have to exist alongside the A-plot power struggle. And they frequently do.
Black Panther is about abandoning isolationism and using a government's power and wealth to help people.
The Avengers have an unmissable theme of not supporting the military-industrial complex. Same with Iron Man.
Common Marvel villains include fascists, bigots, businessmen, and corrupt law enforcement, in addition to the madmen and evil gods.
I've seen this point made a few times, and it just reeks of someone backfilling a reason to hate something popular without actually spending a moment to, you know, watch that thing.