Other LSPs work differently. I know for instance, LNbig only offers inbound channels and you can purchase relatively large inbound channels for cheap.
ThPhoenix came out with something that looked pretty neat, but I haven't tested out. But I think it uses dual-funded channels as well.
I know you can rent inbound liquidity from phoenix and zeus, which I think is the same thing you're talking about. I just tested out making a new channel with a random lightning node. It works! Now I can route payments via zeus or this other random node, whichever is cheaper at the time. Bitcoin is fucking rad,
