I get the thrust of what you say but this wasn't always the case. The idea of linear progress upwards is not universal. Many cultures placed the pinnacle age in their past, before some corruption or decay took place -the ultimate expression of such would be like the biblical story of the Fall, but it also existed on less cosmic scales. The golden age when people were better, seeing your age as decay against the valorized past is in fact more common.
Also just because others thought similar things doesn't mean it isn't true now. The progress since sometime in the 1800s has been insane. If in 100,000 years a super smart civilization, unimaginably advanced, looks at an estimated world population time series, they will be objectively impressed that those guys figured out / stumbled upon some impressive things to manage that. It's really interesting to think about just how desolate the world was even a few hundred years ago. Almost all our big cities today were little towns, except for like 1 or 2 globally. The change is undeniable. It's not all subjective and "they said X, we say X, nobody can decide if X is true, what is truth anyway, etc"
Also just because others thought similar things doesn't mean it isn't true now. The progress since sometime in the 1800s has been insane. If in 100,000 years a super smart civilization, unimaginably advanced, looks at an estimated world population time series, they will be objectively impressed that those guys figured out / stumbled upon some impressive things to manage that. It's really interesting to think about just how desolate the world was even a few hundred years ago. Almost all our big cities today were little towns, except for like 1 or 2 globally. The change is undeniable. It's not all subjective and "they said X, we say X, nobody can decide if X is true, what is truth anyway, etc"