There is one thing I disagree with, and that is evidence of bigger things and lack thereof. Just because we can't see anything doesn't mean it's not there, an advanced species that can travel through space does not necessarily need to leave a fingerprint of their existence, maybe they're hiding intentionally. We only looked at big things, and technological progress is not defined by big things.

I also find the whole idea of a dyson sphere or any similar structure very silly. Who needs all that energy if you're traveling far away through the galaxy? All you'd need is a powerful energy source on the space ship and an optimised way of using that energy.