To be fair, even though Nadal may have missed out on some slams and some potential extra slam titles, you can't really say a player with 16 slam titles (let's not forget that's second in the open era) was really hindered by his injuries. They didn't prevent him from racking up an enormous amount of slam titles, four #1 finishes etc.
Nishikori is clearly a lot more hindered, but I don't think he's good enough to ever build the kind of momentum to win big titles consistently. He actually hasn't won a single big title, and made one Masters (granted, could have won that) and one slam final. He has few other standout results, which I think has a lot more reasons than just injuries, as good as he can be. Something does lack in his game.
Del Potro is the most hindered for a variety of reasons. I think he's a little overrated in terms of his tennis, so I'm not someone who thinks he could have been a consistent slam winner along with Fedalovic etc like some do. However, he was clearly improving quickly since 2008, won a very impressive US Open title in 2009 and then the injuries did set him back. His absences are just too frequent and consistently long, so much that he loses too much rhythm. He also, more so than the other two, needed to tweak and even compromise his game quite a lot to prevent more injuries, as is seen with his backhand now.
But it's actually players like him, in my opinion, that show Fedalovic have something special that allowed them to dominate the field which I just don't see even a fully healthy Delpo ever doing in his career. There's something mechanically fine-tuned about their games and point construction that other players don't seem to have.