It wasn't that major of a port for the South. New Orleans, Mobile, and Savannah were all busier in terms of exports or imports. Charleston was an excuse for Davis to start his war, nothing more.
Let me show you this map again, and perhaps you can then see why it wasn't a major port for the South.
Yup. You are right. It wasn't all that major of a Port for the South. I wonder why that was? Could it be those laws that routed everything to New York? Could it be that if it could achieve about a 50% greater profit for European merchants that it might have become a more important port?
All the money numbers change with independence. Charleston was one of the closer ports in the South for European shipping, and it would have likely raked in massive amounts of trade as a result of that.