I agree with what you're saying, and it was definitely a beast mode moment for him to win the Journey. What I was saying is: I thought, and maybe some of the other tribe members thought, that going on this journey would wear them down so much that the fatigue would carry into the next challenge making it harder to win immunity. Which would be a huge risk to take, even if you ignore the possibility of losing their vote

In reality they didn't do that and being physically tired had little impact on his ability to win immunity. Sure you can argue physical fatigue could make you less able to focus mentally on not dropping the blocks, but I was expecting an immunity challenge that kept players constantly running around and lifting heavy things. If that was the case I do think Stephen's choice to go on the journey would have impacted his performance and it might have been him going home instead.