We were able to understand the motions of the planets, to predict their orbits, measure their masses, predict eclipses, all with amazing accuracy. The theory even led to actual predictions and later discoveries of new planets, by noting slight differences between the observed and calculated orbits of the outer planets. Einstein's Theory of Relativity was one of the most successful theories ever invented. It revolutionised our ides of space and time. Instead of space and time being absolute and fixed they are dependent on the observer.
Different observers have different space and time.
It was even able to account for some of the very small shortcomings in Newton's theory of Gravitation, such as the precession of the perihelion of Mercury, and to explain the slight bending of light rays as they pass a massive object. It provided an entirely new slant on the motions of the planets. There is no need to invoke gravitational attraction at all. In fact, there is no such thing. It was something we invented to explain our observations.