Yeah I hate it when I'm proved wrong too.
Though really, Dragons aren't dominant because of their typing, it's more because of their stats (and access to moves like Dragon Dance, Outrage and Draco Meteor.) I mean, from bulbapedia, "The Dragon-type is statistically the best type, as its average fully evolved stat never goes below base 95." The averages are
That's pretty freaking strong. And the tiers are fan made and really not very pokemon was meant to be good. That's why you can catch caterpie's early on but not Larvitar.
Also ChrisTom, light refracts in water but it doesn't dissapear it just slows down. It's only at deep depths of the ocean can the human eye not see light. Also light is such an easily manipulated thing, I assume you're talking about visible light but using all different types of objects and materials you can get light to do what you want; Whether it be sepperate into the rainbow, appear larger/smaller to the human eye, flip or reverse an image, create an image, speed up or slow down. Light is really in the eye of the beholder, I mean a Pokemon can just close there eyes in some cases and the light attack would be useless.
If you want to argue for a light type I suggest you take the route of BleuVII since his definition (though I still don't like it) is actually plausible. Your defintion could work as an ability though.