The orbit of planets in our solar system have hinted at missing matter several times -- one time it lead to the discovery of a new planet (Uranus or Neptune, IIRC); one time it lead to the discovery of General Relativity.
Until we either detect dark matter/energy, or develop a theory that accurately predicts the behaviour we're attributing to dark matter we cannot say one way or the other which is the correct approach.
It could also be that we are not accurately modelling EM/SR/GR effects at a large scale, such as how they are warped by the different stars orbiting the arms of the galaxies. Or that when we extend QED/QCD to accelerating reference frames (general relativity) that dark matter won't be needed, just like how QED was formulated by extending electromagnetism/QM to special relativity (non-accelerating reference frames).