For such a life as Einstein’s it is impossible to get all the details in full, and likely some of what I write here will also be in error. It is true that relativity as a term predates the 1905 paper, and that many were hot on the trail of the special theory when Einstein formulated it. The principle goes back to Galileo, who in his epochal book on the two great systems of the world (Ptolemaic and Copernican, published 1632) describes the inability of distinguishing uniform motion from rest by a passenger below decks in a smoothly sailing ship. The contraction hypothesis of Lorentz (and also G. FitzGerald) was entirely ad hoc, designed to explain the null result of the Michelson-Morley experiments. In Einstein’s special relativity, the contraction follows ineluctably from the 1905 postulates. For the most part the others looking at special relativity were primarily mathematicians (Lorentz is the great exception), whereas Einstein’s vision was firmly rooted in natural phenomena. To say that the gravitational field equations a decade later were developed by Hilbert simultaneously with Einstein is baldly true; but Einstein had tutored Hilbert in all he had learned and hypothesized over the previous four years or so, at which point Hilbert had the theory all but served up to him on a platter. For Hilbert, then the greatest mathematician alive, the derivation of the field equations (from a Lagrangian) was pretty much an exercise. (Even Hilbert needed help a year or two later with Einstein’s theory, and got it, from the woman Einstein described as “the most significant creative mathematical genius thus far produced since the higher education of women began”, the algebraist Emmy Noether.)
I’m a retired high school physics teacher, and my knowledge of history is modest. Most of the scholars I’ve read believe that while we might have gotten special relativity within a few years if Einstein had not been born, the general theory was the work of one man, though with a mathematical assist. Early on, Einstein’s old friend Marcel Grossmann, who unlike Einstein, had attended their college lectures on differential geometry, helped him with his math. I also think that Dr. Mack is overestimating Einstein’s connection with other physicists. The technical people in the patent office were typically engineers, not theoretical physicists. It’s been suggested that before his first academic appointment in 1908, the only physicist he saw on a regular basis was in his own mirror.
Finally with respect to Einstein’s sexism (an unfortunately near-universal attitude among men of his generation), it should be pointed out that he wrote a stern letter to The New York Times (published May 4, 1935, quoted above) upbraiding them for not affording Noether sufficient notice following her recent death. Like many Jewish scholars, Noether was forced to leave her position at a German university (Göttingen) and come to America. Sadly, she was not offered a position at Princeton, owing to her sex, though she was a frequent visitor. Fortunately, Bryn Mawr was not so far away, and they were very glad to have her.