I remember reading an article 5 or 6 years ago about Tony Hawk, a pro skateboarder. I don't skateboard, so I don't remember the specifics, the overall gist of the article was pretty interesting.
The author outlined several records which Tony had set. He'd been the first to perform a fair number of skateboard tricks - he'd set the bar at the world level. However, after he proved that certain tricks could be performed, many other non-pro level skateboarders were able to replicate his success.
The author essentially concluded that Tony was not necessarily the best skateboarder in the world, but that he had the vision to try and perform tricks and moves which others simply didn't. They would copy him after he "invented" them, but did not innovate themselves.
And thus, you have your answer. If magic is largely a self taught discipline which is sufficiently difficult to learn, then it's quite likely that most practitioners simply never envisioned magical applications on a large enough scale, or did, but didn't personally have the ability to pull that vision off.
Similarly, sometimes a "simple" goal can be achieved in a very convoluted way. It can become ingrained in a society that said process is done in that way, and no other, until an outsider points out that there's actually a very easy way to achieve that result if you only tackle the situation differently.
And so, your hero might be the only person to realize that in order to cast a spell you need not necessarily tap into your own personal energy, but the energy, of say, the Sun, and thus have the ability to do anything you wish.