Steam has nothing to do with multiplayer on PC, at least not in the way you think it does. Steam is essentially a DRM check for this game.
On the PC it's the same stupid peer to peer lobby system as a console. You start the server, so you are the host.
Your multiplayer problems with Red Orchestra and mods/maps/downloads are through dedicated servers. With dedicated servers the admin can load whatever content that's allowed, and configure the game to how he wants it to run it. Much like our Race Department racing servers.
It is precisely because the Codemasters F1 games don't use dedicated servers, that makes the game such a piss-poor platform for multiplayer and competition in general. There is very little control, and the network quality is only as good as the host's connection. Dedicated servers are hosted on high quality hardware and have tons of bandwidth.
Quality of racing? Well personally I would
never join a random open public server (whatever the platform), they are mostly full of griefers, rammers, and 3 lap sprint races.