This is historically not true. Einstein didn't work in complete isolation nor was he the first one to come with a geometric description of gravity. See for instance, [Nordström's theory of gravity](https://en.wikipedia.org/wiki/Nordstr%C3%B6m%27s_theory_of_g...).

This does not intend to take any little bit of merit from Einstein's gigantic contributions, it just come to show the point that Katie Mack is making about the role of community driven refinement. Nordström built on Special Relativity and Einstein's ideas to build a geometric theory of gravity, this one turned out to be incorrect as it didn't predict the correct amount of light bending or perihelion precession. But some slight changes produces the correct one. Nowadays we know that Nordström's theory got only one thing wrong, it's a scalar theory of gravity. Change the spin of the gravitational field to spin 2 and you get Einstein's theory.