With plate tectonics there was the major clue with how the outline of South America fits so neatly into Africa, and I assume that it was known that the rocks were similar on each side of the ocean.
Nevertheless, if the idea remained speculative till the sea-floor spreading was observed then I suppose it had to wait till we had robust enough subs to get down there to see it.
The Gregorian calendar is really the problem because it amplifies relative numbers. The agricultural evolution that started modern humans as a culture was 10,000 years ago. If we think of the current year as 12,025 ME and Copperncian revolution as 11,514 ME I think it puts in a proper scope as all relatively recent and contemporary event.
Gregorian calendar is like standing too close to a Monet or pointillist painting, you lose the scope of the big picture.