There are all kinds of heroes and villains characters in comic books. Some have epic origin stories making them legendary, or epic powers - like Superman. Some have less "wow!" origins and beginnings.
Like, for instance, a young science geek who was bitten by a radioactive spider and gained spider-powers. This is not the most engaging beginning for a hero. Nor a power-set that would at first sight destine him to fight to save the universe. And his tag-line his "friendly neighborhood super-hero". But he became one of the most beloved and complex heroes.
The Hulk is just, in the beginning, a scientist who, after exposition to gamma rays, has the uncontrolled power to change into a big green megastrong, indestructible, stupid colossus. And he can't control neither his "power" to transform, nor what his transformed self does.
Or let's take Shadowcat, because I am a fan. It was just a young girl with the power to become intangible. A mascott for the X-Men. Who would have thought she would become one of the more popular X-men, lead her own team of misassembled heroes, save the universe, and even team-up with Spiderman in an alternate time line/ book line ?
What makes a super hero memorable is more than his origins/begginings backstory, but the stories he is in, the issues he is confronted to, and what "life" and meaning the writers can give him.
Of course, as the SotM heroes and villains don't have a line of comic books to fully "fluff" them, we, players, are in the same position as someone who would look at the beginning backstory of Spiderman without knowing anything else about him, and would wonder what the fuss is. Untill we can see them in play, read the fluff text on the cards and see the art. Then it will help our imagination to "connect" with the submerged part of the SotM iceberg - all these fictional hundreds of comics >G has planned as the background of the game.
I don't react in the same way with all heroes - I find some "lackluster", simply because, at first sight, they are not the kind of heroes I am interested in, from a story point of view. And other players will find other heroes uninteresting. I am a big fan of the Scholar as a character, for instance, (and I can easily imagine the kind of storytelling he can be used in) - but I know that some other players on this forum find him ridiculous. I feel no interest, right now, for K.N.Y.F.E. or The Naturalist as characters, but that's fine, I feel no attraction to Cable or the leader of Wakanda either, but they are part of the whole story and have their place in it.
All this wall of text just to say that even if I don't find all the heroes backstory engaging or "strong", I am very satisfied with the "big picture" of the multiverse as a fictional comic book line written by many different authors for many different audiences. But everyone can react according to his tastes and preferences - I just do't think that any hero we have is a "writing failure", just a facet of the multiverse we may not like.