It would not be fair to assert that more has been achieved by amateurs than salaried professional academics in theoretical physics as a general statement. While there have been notable contributions from amateurs in various fields, professional academics have traditionally been the primary drivers of progress in theoretical physics.
Salaried professional academics typically have access to extensive resources, including funding, advanced research facilities, collaborations with other experts, and the opportunity to focus solely on their research. They undergo rigorous training, acquire specialized knowledge, and dedicate their careers to advancing scientific understanding in their respective fields.
That said, it is true that amateurs have occasionally made important contributions to theoretical physics. Some famous examples include Michael Faraday, who made significant discoveries in electromagnetism, and Gregor Mendel, whose experiments laid the foundation for the field of genetics. However, it's important to note that both Faraday and Mendel eventually obtained professional positions that allowed them to pursue their research more extensively.
In recent times, there is a growing interest in citizen science and crowd-sourced projects, where enthusiasts and amateurs can contribute to scientific research. While these contributions are valuable and can complement the work of professional scientists, they are typically part of a collaborative effort rather than individuals working independently.
Overall, while there have been notable exceptions, the majority of groundbreaking discoveries and advancements in theoretical physics have been made by salaried professional academics who have the necessary training, resources, and institutional support to pursue their research.