Hardly.
By the time of the constitutional convention in 1787 most Northern states had already begun to gradually abolish slavery, the rest would follow soon after.
So, our Founders' vision -- including that of such Southerners as George Washington, Thomas Jefferson and James Madison -- their vision in 1787 was of gradual, peaceful abolition, lead by the states themselves.
After all, that was in process at the time.
Some Southerners insisted slavery must be acknowledged in the Constitution, as their price for ratification, and so it was done.
Other Southerners like Thomas Jefferson insisted international imports for new slaves could be outlawed, and Jefferson also proposed abolishing slavery in the Northwest Territories, which was done.
So, slavery in 1787 was seen as a dying institution to be slowly restricted by Federal government and in due time abolished by the states.
jeffersondem: "And now, you tell me the North had the moral high ground because only 9 of the original slave states were in the North."
First, by 1787 seven of nine Northern states had already begun to abolish slavery, plus what would become five more states in the Northwest territories -- Ohio, Indiana, Illinois, Michigan & Wisconsin.
New York & New Jersey began abolition by early 1800s.
But gradual abolition's "moral high ground" was shared by many in 1787, North and South, including as I mentioned Washington, Jefferson & Madison.
Other Southerners insisted they could not ratify the new Constitution unless it included language on the return of fugitive slaves, and so that was done.
Again, in 1787 slavery was thought to be dying a natural death, and Federal government could be useful in gently pushing it that way, as for example in the Northwest Territories.
“Some Southerners insisted slavery must be acknowledged in the Constitution, as their price for ratification, and so it was done.”
I concede your point: at the time the Constitution was adopted, only 13 of the original 13 states were slave states. And of the 13 slave states, only nine were in the north. And of the nine northern slave states, only nine voted to include slavery in the Constitution.