The point was to punish and keep the South less progressed than the North. That was the original intent of the 3/5ths person and the war. Most of the big investors in big southern plantations and slavery were Northern business.
Had Lincoln lived the recovery may have been better, sooner. It is often reported that Lincoln intended to ship the slaves back to their homeland, if that had been true it would definitely prevented a lot of discord, crime and poverty, even today. As it now is America may never pay off our pay-back.
I think the damage was done when the slaves were brought over from Africa to the Americas to begin with. That cannot be blamed on the U.S. IMHO. Slavery was started under colonial rule and was ended by the U.S. Some would argue that slavery should have ended right at the beginning of our nation’s finding. But we had to get through two wars with the greatest military power on earth, not to mention periodic conflicts with the Indians first.
The net effect of the 3/5ths rule was to give the South a disproportionate level of representation in the House. How did that punish the South?
Since they weren't slaves anymore, whether that was true or not was irrelevant. Couldn't ship them anywhere without their agreement.
Lincoln, in common with a great many other white and a few black men, fantasized about sending volunteer free blacks back to Africa or to Haiti or Central America. Note the volunteer part.
They even made a couple of abortive/disastrous attempts.
Whole thing foundered on two key point: 1. Very few blacks were interested. 2. The costs would have been ridiculous. Even today, in an immensely more wealthy country, the costs of shipping 12% or 15% of the population to another continent and getting them going economically would be crippling.