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Healthy Nuka~! I see so few of these...
On that note, I am one of those people who don't see Nuka as being Scar's son.
Granted, Nuka does insist that HE should be the Chosen One due to being the oldest, but never outright claims to be Scar's eldest child. In the second movie, Nuka refers to Scar by name, and he doesn't seem particularly broken up, on a personal level, about Scar being dead.
Nuka obviously has issues with 'Being good enough' at anything, especially in his mother's eyes.
If Zira was obsessively devoted to Scar and actively sought his approval, than Nuka must've come to the conclusion that if Scar approved of him enough to name him future king, then that would make his mother proud.
However, Nuka was obviously born during Scar's reign, when Zira couldn't get enough to eat and resulted in her son being born weak and then not getting enough to eat himself, growing up weak as a result.
Just my thoughts, sorry for rambling.