In his book Einstein uses tensor notation to write out his equations.  Tensor notation is very very deceptively compact.  Using tensor notation to write out Einstein's field equations is like saying Hamlet’s famous soliloquy is: "To be or not to be", and expecting people to know the rest of it. Einstein’s equations are not friendly, when not written in tensor short hand they are very long and very complex; because of their length and complexity when those of them that can be solved are being solved, they have enough room for errors in which to park a semi-trailer.

Does making equations very complicated make them more correct ?
No, and usually it is the opposite, the more complex the equation the more room for error.

Physicists and Mathematicians love Einstein's equations because they allow for a huge amount of discussion over results that are completely unverifiable, hence no-one is wrong, and the discussions, lectures, papers, research and (grant and salary) money can keep flowing forever.

To be the most generous possible let us assume that in doing the math Einstein and the editors of his book who checked that math, got it right.  On the assumption that the math was done correctly, is Einstein's math treatment of the universe real science ?  Let us look at what Einstein wrote in pages 95 to 103 of his book.