However, saying 'there is x amount of unobservable stuff there' in order to make our calculations correct seems like lazy science. "Dark matter" and "dark ener

However, saying 'there is x amount of unobservable stuff there' in order to make our calculations correct seems like lazy science. "Dark matter" and "dark energy" don't refer to unobservable things, just to things whose existence we suspect but which we have not yet been able to observe. The planet Neptune was once in that category, as was the neutrino, and both of them were predicted "backwards" from a discrepancy between theory and observation (the observed orbit of Uranus didn't match what theory predicted, and it turned out the gravity of as-yet-unobserved Neptune was the cause; beta decay appeared to violate conservation laws, and it turned out the as-yet-undetected neutrino accounted for the "missing" energy and angular momentum).