There would have been no USA if the Founders had insisted on an immediate end to slavery.
You’re right. But here we have people arguing for the “immense wisdom” (to the point of claiming infallibility) of the Founders when they saddled generations with that madness that would end with a Civil War and a century more of 2nd class citizenship for the racial group in question. The Founders were right about some things, wrong about others, and the rest had to unfold to determine right or wrong. The 17th remedied a problem to something that just hadn’t worked out.