I'd also argue that the Erie Canal actually helped southern commerce generally and New Orleans in particular because its creation helped settle the Old Northwestern territories. These settlers then used the Mississippi river to conduct trade with the south.
In his historical work, Charleston's Maritime Heritage, P. C. Coker, described the decline of Charleston as one of the top three ports in the early 1800s.
He cited several reasons for its decline, none of which you mention.
He did state that the construction of the Erie canal contributed to the decline of the Charleston freight traffic because the Erie connected New York to the midwest market.
But your attempts at 'argument' sound more like notions than logic and knowledge.