You can doublecheck each available perk of each weapon before crafting them, so the result is never an "unexpected waste of ressources". You're meant to stick with a random roll you enjoy for a long time up until you're unlocked enough of its pattern to craft a "perfected" version of it (enhanced perks and stats for you). It's a safeguard for the unlucky guardians: If you spend your 240 spoils of conquest on one weapon for a chance at a decent roll, odds are that you'll receive several "lucky ticket" red versions of it. Redeem enough "lucky tickets" for a version that can have anything you want on it.