Okay, let me start off by saying... you've got the folder configuration incorrect. Since all you're doing is overriding files (nothing added, so far as I can tell)... there's no need for the 'Manifest' section in your mod.json.OK.
Everything else seems to work -- but when I added the weapons folder and the line to mod.json, I get the error I described above.
Haven't even changed any of the weapon files yet, this was just to make sure the new folder and files didn't have an issue.
Creating a (pair of) sub-folders in your 'DragonTest' folder named 'StreamingAssets\data' and THEN moving each of those other four sub-folders into the 'data' sub-folder, fixed that issue right off.