Unlike the special relativity, which was just a new interpretation for facts and formulae already established by others (like Lorentz and Poincare) in electrodynamics, so it can hardly be called as "big leaps", and which was fully developed also only by others, like Minkowsky, the general relativity, which was developed more than a decade later, was the most original work of Einstein, being a completely new mathematical model of gravity and inertia. Nevertheless, if Einstein had not existed, it is likely that Hilbert would have become the author of the general relativity.
However the general relativity has no relationship with the equations of Maxwell discussed here.
While general relativity is the most original work of Einstein and the one best known, the second most original work of Einstein is the one that had the greatest impact on practical technology: the discovery that for computing the properties of electromagnetic radiation one must take into account also the stimulated emission (like in lasers), not only the spontaneous emission and the absorption.
For me, Einstein's paper on stimulated emission is the most important of his work. Even if more than a century has passed, it is not yet clear if Einstein's mathematical model is the best for gravity and inertia or if there exists another model that would be more comprehensive and which could relegate Einstein's model to be an approximation that would be no longer useful.