I can't be bothered finding the scan but I'm pretty sure Obito stated Uzumaki have large chakra reserves. Nagato's feats and Kushina still being able to subdue Kurama after having him extracted from her should be enough proof. Add the fact that every previous jinchuuriki of Kurama was an Uzumaki.
Ah, I'll rephrase then; the only people fit to become Kurama's jinchuuriki who are from Konoha/have close ties to Konoha are the Uzumaki.
They were the perfect host because of their incredible longevity and life force.
You can say that for Nagato, but Naruto and Kushina? I doubt it. Yes, they have large reserves, but Uzumakis are known for their distinct 'Life Force' if anything, which is why Kushina survived. The term Large is quite relative. Naruto's base reserves are no where near Nagato's. This is proven from the start of the second part:
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. Which means at the best, his chakra reserves are about four times more than Kakashi's, as he uses the term at least here? And Kakashi's reserves according to kakashi himself, are quite little -
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.
Again, Kurama was kept as a political leverage not to make Jinchurkis out of Uzumaki. There is no manga evidence to back this up. True, Kushina and Mito were good hosts, but that is ridiculous to assume that they somehow represent the entirety of their Clan.