This stuff FITS REALITY to many decimal places.
Newtonian mechanics predicts planetary orbits to 6 decimal places.
Einsteinian mechanics predicts planetary orbits to 9 decimal places.
Einsteinian mechanics predicts bending of light around gravitational fields.
Consider GPS. When originally designed, some of the engineers involved thought that using General Relativity was pointless. They were shown to be DEAD WRONG. Without GR corrections, GPS drifted several kilometers per day and nothing could be done about it. WITH GR corrections, drift is negligible and easily eliminated.
The problem is that time goes FASTER for a spacecraft high above the Earth than a stationary observer measures on Earth. This is with the SAME kind of hyper-accurate atomic clocks. The clocks are not the issue. The CURVATURE of space-time is the issue.
This makes Einsteinian mechanics BETTER than Newtonian mechanics.