Dude, if you genuinely want to know what happened, you should read some proper history of science. Here take this: https://arxiv.org/pdf/physics/0405066

It shows both how Einstein very much didn't make the theory alone, was inspired to take impotat technical steps by work of other thats that created a theory based on his principles before him, and that actually he first created (in intense collaboration) a failed theory that got Mercury's anomaly all sorts of wrong.