To put it another way, Einsteins discoveries were HUGE, however they were also inevitable.
Not only inevitable but the pieces of what he said were likely already being put together by others.
Had Einstein not existed, chances are people would be arguing that "Silverman" deserves to be on this list, or whoever else shortly made the discovery afterwords.
Not to say such things aren't important, but when it comes to the most important achievements and people of all time, I think the inevitability of such a discovery should weigh heavily.