I don't understand where you have read they will be "relying on the ability of the Bitcoin blockchain"

Greenbacks have his own blockchain, so why should they care about the bitcoin blockchain and their devs?
In the whitepapaer they themselves stated the good thing in bitcoin is the infrastructure & community around and not the specs themselves which are pretty outdated and frustrating
Looking forward to the new wallet, seems cool although i don't really like this green design