There’s a much bigger difference in ability going from a 2:30 marathon to a 2:00 marathon than going from a 3:00 to a 2:30 marathon. It’s not linear. But it’s a

There’s a much bigger difference in ability going from a 2:30 marathon to a 2:00 marathon than going from a 3:00 to a 2:30 marathon. It’s not linear. But it’s also not relevant to the point the OP is making.