If Hayden had never played Anakin some other young whippersnapper's potential career would have been devoured by the lousy dialogue.

Hayden showed some mild promise in a couple films (Shattered Glass, Life as a House), but as an actor he's interchangeable.

My view on actors is that virtually all of their performances depend on the director and script. There are acting legends like De Niro, Caine, and those types who can certainly direct themselves, but in most cases it's the director that makes the performance.

Not to mention most young actors are basically models with no acting experience or training. Anybody can act. Some can act well with the right circumstances. Few are exceptional.

Just look at Portman. She's arguably the worst in the prequels. She probably didn't try hard anyway, but still you can see the difference a good script and clear direction can make.