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Astronauts are people at peak fitness selected out of a massive sample size, so they're way above the average modern human in physical prowess, while 'caveman' does not indicate any equivalent elite status. Modern humans are considerably taller than their ancestors, so that's a significant advantage in reach, and when combined with the benefits of a complete and plentiful food supply through your whole adolescence that comes out to a pretty huge strength advantage compared to people who were almost certainly malnourished.

On the other hand, a caveman has probably killed animals and potentially other people just to ensure their own survival, while relatively few astronauts even study martial arts for recreation. Which means that the caveman could overcome their significant physical disadvantages by escalating to violence quickly, suddenly, and without any reservation while the astronaut is still trying to assess the situation. It could go either way, depending primarily on the personalities involved.

Another Fact: Link still has the Master Sword in Super Smash Brothers. Brawl has the cutscene where he draws it from the pedestal again but in the other games he just Has It