One advantage to paracord that I can see is that since it is synthetic it is less prone to deterioration due to elemental exposure. Natural products are far more susceptible to breaking down over time. Of course we should be checking the condition of items in our kits regularly, but I think the natural cordage would not be as reliable...have to pay more attention to it in kits than paracord.

Another thing, as far as shelter building or repairs is that the tensile strength is much higher than most things we will require as far as shelters or repairs. This can lead to the confidence that our shelters or repairs will not fail due to the cord breaking.

Paracord has the smaller strands inside which can be used individually as well as the outer sheath which can be used with or without the inner strands. This has versatility advantages that single strand cordage does not.

Test the jute and sisal in as many situations as you can. Build a shelter in your yard binding it with the natural cordage and another with paracord. How does each one stand up to the elements? How does long term direct sun affect each? What happens when they get wet, or freeze?

Remember, survival equipment is not an area to pinch pennies in. If jute and sisal fit your budget better than paracord right now, then go with it. I'm constantly upgrading components of my kits as money allows. But having something in place is better than having nothing in place...even if it's not your ideal piece of kit.