The vault was purposely designed to allow gear and resource sharing. I don't think it's a far stretch to assume that this is exactly what the devs had in mind. One reason for this, and this is my theory, is this is another way to keep you playing. For me, I was not going to create multiple characters, but...after playing my hunter for awhile, and accumulating gear for other classes, I decided to make a warlock and a titan. YOU believe this to be an exploit, an oversight, yet, the vault was purposely designed for this very thing. Glimmer is shared, resources are shared, vault is shared. These are on purpose designs. This is hardly an exploit. Pushing a boss off a cliff? Exploit. Using the vault the purposeful way it was designed? Not an exploit.