Comic books have used every possible genre type in their pages, but super heroes are the one genre which comic books themselves gave birth to; for virtually every other genre represented in comic books there is a clear source of adaptation from another medium, be it prose, film or dance. When Superman debuted in Action Comics #1 he was essentially the first super hero - or at least the first character whose attributes fit those we came to associate with super heroes: he was powerful, wore brightly-coloured tights and used his power to help the defenseless. As the super hero genre came from comic books it makes sense that they dominate the medium...
...To the extent that the medium persists, that is. Super hero comic books hit a peak thanks to World War II as many of them (such as Captain America) were created specifically to combat Hitler. With the war's conclusion, the heroes struggled to define their goals and audiences lost interest. The genre picked up some steam in the 1960s and finally broke out in a big way due to the hit 1989 film Batman, but within a decade of that picture the industry nearly slit its own throat as a speculator-based comic book economy crashed; comics retreated to their familiar niches.
Today, sales of super hero comic books are in a state of constant decline as the corporate owners try desperately to reignite interest in the characters by changing their powers/origins/genders/ethnicities, only to eventually succumb to the inherent entropy of the audience. The arrival of a Captain Marvel motion picture has a large number of fans stoked; meanwhile, the character's comic book has been on life support for years.
Perhaps the super hero comic book business has become too insular, too repetitive, the same ideas played out over and over by increasingly jaded creative teams to an increasingly jaded audience. Perhaps it could be instructive to look back to where the genre began, to the creators who originated the super hero tropes which are now being subverted, deconstructed or taken for granted. The early super hero comic books were crudely made and would happily cannibalize each other's ideas even as today's arguably do. But for Captain America's creators Joe Simon & Jack Kirby you see a hero designed to face a real threat - not a metaphorical/allegorical stand-in for that threat either - Captain America was created as a response to Adolf Hitler.
This is true as well of Joe Shuster & Jerry Siegel when they originated Superman. Look to the first appearance of Superman and you find a hero very concerned in the issues of the time for the prewar US. In Action Comics #1, Superman has four separate unconnected adventures in a mere 12 pages! First, he prevents an innocent person from being executed; second, he rescues a woman from her abusive husband; third, he battles organized crime; finally, he combats war profiteers.
The concerns of the USA in the late stages of the Great Depression are not the same as those which we have today. In some ways, super hero comic books of today are still grappling with issues of late 1930s USA, such as their conception of organized crime or foreign wars. But even there in Action Comics #1, Superman was concerned with upholding legal justice (preventing an innocent woman from being executed) and social justice (turning the tables on an abusive husband).
At times I wonder if super hero comic book creators can see the trees from the forest. In the past, there was certain content which super hero comics could not (nor should have) addressed directly, but today there is no particular subject matter which ought to be avoided, particularly as the super hero genre is read overwhelmingly by adults, not children. At one time, it made sense to discuss racial troubles through the metaphor of mutants, as the X-Men did; but today's issues surrounding race would be better served by telling stories about those races and their difficulties.
If you want to write a super hero comic book but don't want your voice to be lost in the throng of a hundred other voices, this is my advice to you: Write about the time and culture which you live in. Do not think that the problems of today cannot be overcome because, after all, Simon & Kirby witnessed the fall of Hitler. In spite of it all super heroes have a capacity to inspire audiences, even the jaded Wednesday warriors at your local comic book shop.
My sincere thanks to Jerry Siegel & Joe Shuster for granting comic books a character, a genre and a whole system of tropes which have kept this lovely medium afloat over the last 80 years.