> It seems impossible to implement true decentralized routing, so it's likely they're using some sort of hack to prioritize "masternodes" as the backbone routers instead of actual peer to peer routing.

What do you mean "impossible to implement true decentralized routing"? Many examples of decentralized distance vector and link state algorithms exist. I'm not sure what they are doing but routing isn't some mystical thing that requires a master node.

Here's a thing I did a while ago: https://github.com/jtremback/reactive-payment-routing