All of the advances of modern physics were made by people who were well trained and well acquainted with the state of the art.
There is a myth that Einstein was an outsider. He had a degree in physics. He was working as a patent clerk because he couldn't find a job as a high school teacher, not because he didn't know physics.
One of his earliest great works is one that indicated wrong in the foundational aspect of the theory, namely incompatibility with E&M Maxwell equations and Galilean Transformations and E&M equations not being invariant under those transformations. The principle of symmetry is one of the foundation issues in physics. He also had th wisdom of understanding of the physics of new transformation, Lorentz transformation, which we know today as Special Relativity.
Yes, of course he was well-trained and had the enough background, but also the problem at the time was the type of problem that was solvable (i.e. no limitation in terms of tech) and that required new framework with new understanding.
There is a myth that Einstein was an outsider. He had a degree in physics. He was working as a patent clerk because he couldn't find a job as a high school teacher, not because he didn't know physics.