Stronger? Then it's still footballers. F1 racers are short and skinny. They're 165-175 cm tall and are on a heavy diet to keep their weight down. The only part physically stronger on a racer is their neck muscles.
Fitter? They both have to fit. But since a football match and a GP take roughly the same time and a footbaler uses twice as much energy during that time, then saying racers have to be more fit is kind of far fetched.
Tbh, it seems you're just changing the question so that you'd be right and you're still not. Next time say "oh yeah, I meant mental strength, damn my English". Then I could agree that it's the racer.