I suspect he's right, although there are acres of Adams I have not read. Still, he can be pretty expressive at the beginning. Here's Adams on life in the United States around 1800:
Nearly every foreign traveller who visited the United States during these early years, carried away an impression sober if not sad. A thousand miles of desolate and dreary forest, broken here and there by settlements; along the sea-coast a few flourishing towns devoted to commerce; no arts, a provincial literature, a cancerous disease of negro slavery, and differences of political theory fortified within geographical lines,--what could be hoped for such a country except to repeat the story of violence and brutality which the world already knew by heart, until repetition for thousands of years had wearied and sickened mankind? Ages must probably pass before the interior could be thoroughly settled; even Jefferson, usually a sanguine man, talked of a thousand years with acquiescence, and in his first Inaugural Address, at a time when the Mississippi River formed the Western boundary, spoke of the country as having "room enough for our descendants to the hundredth and thousandth generation." No prudent person dared to act on the certainty that when settled, one government could comprehend the whole; and when the day of separation should arrive, and America should have her Prussia, Austria, and Italy, as she already had her England, France, and Span else could follow but a return to the old conditions of local jealousies, wars, and corruption which had made a slaughter-house of Europe?
The mass of Americans were sanguine and self-confident, partly by temperament, but partly also by reason of ignorance; for they knew little of the difficulties which surrounded a complex society. The Duc de Liancourt, like many critics, was struck by this trait. Among other instances, he met with one in the person of a Pennsylvania miller, Thomas Lea, "a sound American patriot, persuading himself that nothing good is done, and that no one has any brains, except in America; that the wit, the imagination, the genius of Europe are already in decrepitude;" and the duke added: "This error is to be found in almost all Americans,--legislators, administrators, as well as millers, and is less innocent there." In the year 1796 the House of Representatives debated whether to insert in the Reply to the President's Speech a passing remark that the nation was "the freest and most enlightened in the world,"--a nation as yet in swaddling clothes, which had neither literature, arts, sciences, nor history; nor even enough nationality to be sure that it was a nation. The moment was peculiarly ill-chosen for such a claim, because Europe was on the verge of an outburst of genius. Goethe and Schiller, Mozart and Haydn, Kant and Fichte, Cavendish and Herschel were making way for Walter Scott, Wordsworth, and Shelley, Heine and Balzac, Beethoven and Hegel, Oersted and Cuvier, great physicists, biologists, geologists, chemists, mathematicians, metaphysicians, and historians by the score. Turner was painting his earliest landscapes, and Watt completing his latest steam-engine; Napoleon was taking command of the French armies, and Nelson of the English fleets; ivestigators, reformers, scholars, and philosophers swarmed, and the influence of enlightenment, even amid universal war, was working with an energy such as the world had never before conceived. The idea that Europe was in her decrepitude proved only ignorance and want of enlightenment, if not of freedom, on the part of Americans, who could only excuse their error by pleading that notwithstanding these objections, in matters which for the moment most concerned themselves Europe was a full century behind America. If they were right in thinking that the next necessity of human progress was to lift the average man upon an intellectual and social level with the most favored, they stood at least three generations nearer than Europe to their common goal. The destinies of the United States were certainly staked, without reserve or escape, on the soundness of this doubtful and even improbable principle, ignoring or overthrowing the institutions of church, aristocracy, family, army, and political intervention, which long experience had shown to be needed for the safety of society. Europe might be right in thinking that without such safeguards society must come to an end; but even Europeans must concede that there was a chance, if no greater than one in a thousand, that America might, at least for a time, succeed. If this stake of temporal and eternal welfare stood on the winning card; if man actually should become more virtuous and enlightened, by mere process of growth without church or paternal authority; if the average human being could accustom himself to reason with the logical processes of Descartes and Newton!--what then?
Henry Adams, from "American Ideals" Chapter 6 of
History of the United States: The United States in 1800
Note that "1800" equates to the final year of the Presidency of John Adams, Henry's distinguished ancestor. There's a splendid hypertext edition of "The United States" in 1800" here.