Well, his biggest mistake is that there is a fundamental incompatibility between relativity and quantum mechanics.
His theory of locality, while it is a nice, pie in the sky sort of thing, is wrong.
Bell showed that either Einstein was right or quantum logic was wrong, and Quantum logic has been proved again and again.
He also proved that there was no “hidden variable” theory that could mitigate the differences between Einstein’s view and quantum logic.
So Einstein was flat out wrong... and God, does indeed, play Dice!
If he places dice, he has also occasionally played with loaded dice, as when God in matter flesh came and died for our sins.(God’s thumbprint pressed into matter. The house always wins!
The media needs a single “greatest of all time” to the exclusion of anyone else for its simple-minded messages to its siumple-minded audience.
So Picasso, even though much of his work is work is gibberish, is chosen as the only painter.
Ali, who was a mediocre heavyweight fighter as compared to the best heavyweight champions, is rabidly promoted as the media’s “greatest of all time.”
Einstein is the media’s choice as the single scientist and “smart man.” To hell with any other mathematicians and physicists.