That's a false equivalency. The weapons are obviously inspired/based on real-world designs and concepts. The Traveler is not... unless you count basically being a GOD to be a "real-world" comparison.

IDK it just doesn't make sense to me that you would put so much effort into this post that matters so little. What if we find a more efficient gun design in the future?

Then it would probably be used in every instance. Such as with shotguns. But it's not, shotguns in Destiny are basically just... shotguns. Also, Hawkmoon would be considered a less efficient design by that logic, if the design of all the others is "better". I highly doubt misaligned mechanical objects will ever be "more efficient". Even in the Chiappa Rhino, which many people insist is how the hand cannons in Destiny work (disregarding animations), the design is less efficient than a standard revolver. There are more moving parts in the Rhino due to the double hammer/cam design.