> 2000 years ago people were on the right track that the Earth is round but couldn't "test it" but going around it.

Fun fact: Eratosthenes measured the circumference of the Earth and the tilt of its axis around ~200 BC, by comparing the angles of shadows at two locations. Perhaps not definite proof, but certainly a test of an assumption.

https://en.wikipedia.org/wiki/Eratosthenes

This is not to disagree with the thrust of your argument, however :)