Naruto broke down when neji died, luffy however tried to re-form his crew when they got separated regardless of how hard it was since kuma had sent each of them in different parts of the world(paradise). Even when his own brother died in the war he only showed fury and extreme anger, but he hadn't gave up.Hell luffy had climbed a mountain while holding literary two bodies.Not to mention that he overcame ivankov's shot, which is pretty much torture
There are just so many ways luffy's willpower is presented in the manga.