Unless you make multiple refined copies of something, pretty much every thing you make is a 'prototype'. Sometimes roughing something up in a cheap fabric is a worthwhile practice exercise.
For many items such as tarps, stuff sacks, pouches, gaitors, even packs, the final look of seams is no big deal. Unless you have a double needle machine and the feed attachment it is hard to duplicate the look of factory seams. I find it isn't worth it to make many high-seamage, tight tolerance items such as complex hats, gloves, etc. Mittens aren't too bad.
Many times to make things lighter, fashion features are left out. A pair of pocketless wind pants with no zippers and a bungie cord waist will always look cheap even if the main seams are neat and tight on a good pattern. Lighter fabrics often lack the substance or 'hand' to look form fitting.
Stretch fabrics or panels of stretch fabrics can help with fit, as can using bias-cut pieces to give woven fabrics a little stretch and better drape. Adapting a patern to bias cut is trial and error, particularly for weaves that aren't symetric.
But I suspect the double, parallel seam or top stitch will always be a tough thing to duplicate on a hobbyist sewing machine.
If you want your home made gear to be undetectable, you'll need to make many copies of an item to refine the design and learn how to get around the trouble spots. Then sew on logos, reflective accents, functionless straps, undersized pockets, and use the heaviest, widest, water-holding elastic on every hem. ;-)
Often no one will see the flaws as clearly as you do. I am amazed at how little comment my 'craft made' creations draw.