Except it went up during the war, not afterwards. Face it , in the end it did jack squat. Shipping insurance rates are hardly the be all and end all in an economy. It is only a small part of it.
You seem to be taking this rather personally.
In any case.
The
guerre de course doesn't actually have to do decisive damage - it just has to do worthwhile damage. And really, if the Confederacy had got the balance right, they'd have managed to make the Union send out the OTL number of vessels (fifty or so) to handle a dozen commerce raiders (a smaller number than OTL, but a larger number
all at once than the Confederacy managed to surge OTL).
That does not by itself win the war - but if they did it and then sent out a couple of ironclads, then they could do some fairly reasonable damage. Or, more to the point,
think they could do that damage - and hence lead to a fleet action of sorts.
Heck - have the Virginia be a slightly shallower draft vessel and there's all kinds of butterflies you can get from that. The limiting draft on the Potomac is 24 feet, only a few feet deeper than
Virginia - though of course that involves less guns, thicker armour or a larger ship in general, so it doesn't solve everything.
I suppose I prefer trying to work out how to make something work, in general, rather than slapping a big "ALL WORTHLESS" sign on it and not bothering to consider possibilities.