To understand the Constitution and the period in which it was written, one should start with a dramatic period of change: "The Age of Enlightenment". It is the period that Western Europe and the new American Colonies begin to change their philosophies of governments, people, religion and the purpose of life. The period will dominate the Founders concept of the above.
The founders cherry picked what they wanted from the 'Age of Enlightenment'. Making it a rather unreliable measuring stick. Its probably better to read the philosophy and writings of men of that era in America. Thomas Paine, Alexander Hamilton, Thomas Jefferson. With Locke being a great influence on the the three, with Paine and Jefferson most accutely influenced.
The Age was a period of changing ideas over a period of time
The founders also had a rather profound distrust of direct democracies. They insulated almost every fuction of the government from them. In their original conception of the federal government only the House of Representatives used it. All other branches were populated using parlimentary processes considered by the founders to be more reliable. With State legislatures being the single most powerful agent in the Founder's conception of government.
The states were necessary for the ratification of the Constitution and so it was necessary they be in the picture.
Being 'in the picture' and being the single most powerful agent in the Constitution under the Founders aren't the same thing.
Under the founder's constitution, the people only voted for one half of one branch of government. Nothing else. The people didn't elect the president.
The State legislatures did, through the electoral college. The people didn't elect senators.
The State Legislatures did.
The people didn't elect any members of the federal judiciary. They were nominated by the President,
seated by State legislatures......and confirmed by the Senate,
all seated by State legislatures.
The founders didn't have much faith in direct democracy. While the 'Age of Enlightenment' was far more optimistic about it. The founders were practical men, working with in a specific framework of States that had united for a common defense. And that context informs the constitution as much as the writing of any author of the Age of Enlightement.
The Age of Enlightenment generally provided the moral justification for some of the more marketable arguments of the founders when rebelling against the English. It didn't have nearly as much influence on the government created by the US constitution.