Victor Davis Hanson made a similar point in the book "Who Killed Classical Studies": every significant text has been analyzed in depth, and the remaining texts still being found are minor. (Even if a new play by Aeschylus or book by Livy turns up, it's not likely to change what we know very much.) The historical picture is pretty complete; and the archaeological details being found are mostly refining that picture, not overturning it.

Counterargument: the Antikythera mechanism. There could well be more archaeological surprises, or analyses that open up an entirely new aspect.