How did anyone manage to do it after slavery was abolished? Did the nature of genius change at that point?

Ben Franklin was one of the greatest minds worldwide of the 18th century. Odds are, even without slavery, he would have contributed just as much as he did with slavery. It's not like he made his money working slaves to the bone in a field and couldn't turn a profit without slavery.

He was a publisher. A few slaves were involved but they were largely incidental to the business. As in, he could have easily paid John and Sam a wage instead of paying to feed and house Peter and George and the business would be entirely unaffected