I don't think they needed superheroes or anything else the first season: They just needed to not have eight or nine episodes that were little more than filler. I am the exact demographic for this show, and I had a really hard time watching it after the first few episodes.
This is, frankly, a Joss Whedon problem. He writes strong pilots, strong finales and good tent pole moments around sweeps, and then hands over the other episodes to his team, some of whom do great (think of Buffy's "Hush") but who mostly turn in second-tier work (at best).
Dollhouse was a great example of this: other than the finale, the first season was almost entirely terrible, other than the Patton Oswalt episode. Yes, the network wanted it to be Creepy Sexy Time for the first few episodes, but even the long awaited "episodes that Joss really was excited about" turned out to be ... meh.
The only show I think he's ever done that was zero percent filler was Firefly, which looks more and more like an anomaly as the years go by. Instead of getting stuck with 22-episode seasons, which are obviously more than he has interest or perhaps ideas for, he'd be better off with BBC-sized six or seven-episode seasons that he could back with all A-quality stuff.
The fans weren't wrong about SHIELD, no matter how the actors snarked about it last season: The writing was really, really flabby and, coming off of a number of really tight Marvel movies, that was disastrous.