You have a point, but (irrespective of what GL says) those characters arent called the strongest ever.
On a geekier note, there are bigger fish out there like Revan and Exar Kun, but the will of the force determines what happens in the film.
Anakin is the chosen one, as the prophecy says, and the unifying Force does all it can to make it happen.
These characters arent the strongest ever, there just lucky and take a lot of killing to fufill the prophecy.
Finally, I'm really starting to dislike GL. True, he created Star Wars and he's a pretty good director but he dismisses the efforts of talented writers that have filled in his gaps and many, many plotholes.
It must be frustrating for a SW writer etc. to gain recognition for strong characters (Thrawn) and then for Lucas to say it doesnt happen!