I would agree with it being lazy to judge the people of the past by the standards of today, but being that it took until the 1960s for "equality", I would say it is also equally lazy to credit the founders with this "grand vision" because they didn't have it. In your version of things the least they could have done was not own people personally! However they did own people, which pretty much shows you that the constitution didn't apply to all PEOPLE!
If we don't want revisionist history then let's not revise either way. They were incredibly smart men that gave us a document that was fortunately worded to only need 27 amendments so far! That's amazing, but they were also thought black people were property and women weren't smart enough to vote. Sure that was part of the times, but I think we can all agree that slavery is abhorrent regardless of the time or place in history, especially in a brand new world where you (looking at you rich white men) are writing the rules!
As I've said, amazing visionaries that gave us the constitution, but don't over credit them, they were people of the times and they didn't view slaves as people!
We have what has been and what can be the shinning city on the hill for the rest of the world, but if you believe that we have been a moral beacon to the world, with our upstanding Christian beliefs throughout our history, you are revising history to fit your narrative. The United States is AMAZING and is currently the defenders of freedom, but take off the rose colored glasses and examine our history, we have had plenty of times where we haven't led the world in areas we really should have been leading!