I think Strike started like that, but then later they open their network to the rest. Then using a big wumbo channel with the rest of the network for moving liquidity in/out from that closed sub-network. This could provide a closed traffic between all Strike users, even with 0 routing fees, but when is about to move funds out of "strike network" the strike node will route the payments through their public or other private channels with other public nodes.

Yeah visualizing this as a VLAN or subnets. It's an interesting experiment.