Your example is rather invalid, as Fire is his natural affinity. Ninja can use their natural element without mastering, simply because it comes natural to them to use it the way they do. Like... If you're naturally graceful, then it's easy to twirl around and look pretty, but the rest of us fall over our feet trying to do the same.
Using an element that you do not have natural affinity for and have not yet mastered is very unwise, though I suppose it is not impossible. It would not just be [i]weak[/i], but rather it would be dangerous. Mastering the element is sort of like "taming" it and making it follow your commands. If the element is not "tamed", it'll do what it'll do.
Wind is also one of the most dangerous elements to play around with like that. Water would just puddle to the ground and be useless if not tamed. Fire would simply burn out (unlike what some might think, it would not explode). Earth would just not respond properly and would possibly just, you know, crumble. Lighting and wind, though, are both "sharp" elements that are used as "blades" when mastered. It'd be like throwing a bunch of knives into their air and hoping not to get hit.