What is the meaning or origin of the idiom "a Shakespeare and a Scott"?

I came across this idiom, "a Shakespeare and a Scott," which I have found in several different writings, and haven’t been able to ascertain its origin, meaning, or an appropriate synonym.

"Poetically classic ground does not, alas! occur with us, as on the shores consecrated by a Shakespeare and a Scott." – Sir Samuel Ferguson in the Ireland of His Day, p. 100.

"How extraordinary that a great and powerful empire like Great Britain, uniting as she does every facility and requisite for its cultivation and development, should be so insensible to its value—a country which has produced a Bacon, a Newton, a Milton, a Shakespeare, and a Scott—a country which has excelled in every other walk of human genius and enterprise!" – Remarks on Ancient and Modern Art, pp. 394-395

"The reason why they omit it is that it is impossible for any but a Shakespeare and a Scott to touch it with any kind of life, spirit, delicacy, and truth." – The Token and Atlantic Souvenir, p. 274

Shakespeare is obviously a reference to the playwright, and it appears Scott refers to Walter Scott, a renowned English novelist.

My guess is it is a way of emphasizing the difficulty of a task, capable of being successfully completed only by one with profound intellect and skill, and as for a generic synonym, perhaps genius? Is anyone familiar with this idiom and its origin?