Sympathetic Nervous System vs Parasympathetic Nervous System?

I think the answer is easier than you are making it.
You don't seem to have a problem with knowing HOW the SNS and PNS are working, but are basically asking WHY evolution hasn't made this system better by making the preganglionic fibers of the SNS longer than the the slower postganglionic fibers to increase the speed of the signal.

We have to look at the different functions of the SNS and PNS, and see how they are reflected their structure and composition. One of the big differences between them is that the signals or the SNS are extremely widespread rather than specific to one organ or muscle sheet, as in the case of the PNS. For this reson it makes sense to have the SNS ganglions close to the vertbral column, as opposed to all the way to each organ/muscle.

From what I can remember I believe the reason why there are shorter preganglionic fiber sis because for emergency situations instead of going all the way to the brain and then back down again, they interact only with the spinal cord so you get a more immediate and necessary response.

I hope this helps! Best of Luck! (I do not miss that material!)

Adrenal medulla and Sympathetic ganglia are almost  like ductless glands releasing emergency hormones directly into blood stream  for emergency reaction. The hormonal release is regional and it is not necessary to go all along  from center to periphery.