Imagine we wanted to make an exact copy of the pyramids in Egypt, the great pyramid specifically.
Never mind building them without machines. Do you think mankind, not just the current residents of Egypt, but do you think in this world there exists the technical know how and political will to even be able to do it?
May be a fallacy, but you still didn't name anything significant we use now that could be named a legacy of ancient Egypt civilisation.
No use at all. But civilisations who build them leave not only that artifacts, but also many other useful knowledge and legacy we use everyday.
It seems you've answered your own question with your second response.