It's not just General Relativity -- if there is no dark matter, the very Newtonian gravitational force having an 1/distance² relationship would need to be wrong on large scales.

However, no attempt at formulating a theory that propose a different long-range gravity than 1/distance² (and still reduces to the known behavior in the short range) has held up to observations.

(And with "short" I mean "on the scales inside our solar system", not meters).