Her mutation allowed her to control the weather which sounds tiny until you realize all of the wild things she could do with it. Controlling the wind allowed her to fly, toss enemies around like rag dolls, and even bring down aircraft. Power over the clouds meant she could create spontaneous floods, blast her foes with lethal lightning, and blind everyone with thick fog. Even when her enemies were unstoppable, she would blast them with arctic winds and freeze them solid. The the X-Men had time for lunch and naps before they thought up a plan to stop the bad guy. Storm was great. Too great. She was an "I win" button that made everything way too easy.
There is a man in the Bible who became that sort of legend and powerhouse to the people of God. He too grew up in Egypt. He too performed phenomenal miracles over nature that would cause Storm's powers to look like the magic tricks you see at a child's birthday party. He too was an "I win" button and no situation the people ran into was unsolvable with him around. But Moses didn't start out that way. The movies you've seen may have painted a very different picture than the truth in the Bible. Moses actually starts off as a bit of a loser. So what turned him into the hero we know?