Boltz doesn't route payments. You open a channel to the Boltz node to harvest fees from people using the Boltz service. It's not a public routing node. It's an atomic swap node.

It's the same with Robosats. Their coordinator's don't route payments. You open a channel to a coordinator to harvest fees from users of that service.

Go to amboss.space and search for the nostrich tag. Nodes with that tag are nostr friendly have no base fee making it possible to send small zaps without high fees. That's the type of nodes you want to open a channel to.