Well, isn't that a little too easy? Tennis has a long list of guys with one slam who aren't necessarily any more talented than Nalbandian.
In fact, I don't think even you think Del Potro is more gifted than Nalbandian in which case you should stop arguing as if winning a slam means necessarily you are more talented than an also talented played who didn't.
Further, there are a lot of aspects to talent. Mental focus as well as consistency etc are other aspects of talent just as much as a good stroke.
Anyone is less talented than Nalbandian, except Federer, and hell it's disputable who's more talented of the two at their prime.
Obviously Federer made better use of his talent. Nalbandian did doodley-squat. (He's still one of my fav players).
Delpo is also using the better of his talent. His prospects are pretty great if avoids more injury time.