Earlier quoted context omitted.
Earth being the only habitable planet is incredibly improbable.
We hardly have enough data to say that. In fact we've found nothing remotely similar to Earth in all the thousands of samples we've taken. So if there are any others at all, they number in the dozens?
I'm also not sure that In fact we've found nothing remotely similar to Earth in all the thousands of samples we've taken. is reasonable.
Take Proxima b. It orbits the Sun's closest neighbor, is in the habitable zone (doesn't mean it is habitable, necessary but not sufficient) and is roughly earth sized. Sure, we don't know a whole lot more about it, so it is quite likely to not be a nice destination for humans, but it seems to be at least remotely Earth like.