The "lone genius" is somewhat of a myth, but also has a certain amount of truth to it. For example, Einstein was certainly a lot smarter than the average person - indeed, probably a lot smarter than most highly-accomplished scientists and engineers. However, he also was at the right place at the right time, and would never have come up with General Relativity had it not been for the work of his predecessors, such as, e.g., Riemann, who enabled Einstein to think of space-time in non-Euclidean terms, etc.
I think the biggest problem with the "lone genius" mentality is that it encourages the popular notion that "if it wasn't for Einstein, we'd never have General Relativity." But of course, this is most certainly false. If Einstein never existed, someone else would have eventually noticed problems with Newtonian mechanics over large distances, and ultimately applied Reimannian geometry to spacetime as a solution. It may have happened years or decades later, but overall scientific progress is very rarely strictly dependent on one individual.
I think the biggest problem with the "lone genius" mentality is that it encourages the popular notion that "if it wasn't for Einstein, we'd never have General Relativity." But of course, this is most certainly false. If Einstein never existed, someone else would have eventually noticed problems with Newtonian mechanics over large distances, and ultimately applied Reimannian geometry to spacetime as a solution. It may have happened years or decades later, but overall scientific progress is very rarely strictly dependent on one individual.