Answering the original question: I can't tell about the PS4 version, but I have just fired Assetto Corsa on Xbox One and found a total of only 16 online users participating in three races out of over a hundred lobbies; most are empty. Possibly one of the reasons for this is that you can't create private lobbies, but the situation doesn't seem much better with the PC version: only 7 users in a server in Germany, all the others empty. (For comparison, right now Forza 6 has several thousand users online.)