The OOO driver was probably made when the Greeed were created, thus the two are more deeply connected then simply the driver being made to combat them. It would explain why the lines on Monster Mazool's back/shell had lines similar to the driver. It goes to speculation that the Greeed may have once been humans who over used the driver and thus became Greeed. In order to prevent such a thing from happening to a modern rider, Birth, a limited system had to be created. One that didn't threaten the life of the user, or threaten to corrupt them. We realy won't know for sure until Birth pops in a core medal if he even does. ANd I still say Maki didn't make the Medjalibur, he excavated that **** and took credit for it.
In short, Birth is a limiter so humans can use the medals without being injured or currupted, and the OOO driver is farmore dangerous then what is let on and is far more closely connected to the greeed then what has been shown thus far. LOL for all we know Ahnk was OOO at one point but used the Bird medals to much and ended up a greeed, which would explain alot.