I get what you're saying, believe me. This is just a theoretical debate and I don't think anybody can be proven wrong or right.
But to me, intuitively, the objective of baseball is to get a lead and then keep it. Score early, then prevent.
If in the hypothetical world a manager had Derek Jeter and Mark Belanger on his team, how would he use them? I think the majority of managers would play Jeter for the first 6-7 innings of a game and Belanger for the last 2-3 innings.