It wouldn't have to keep track of them though. Say I'm in Gr.3 car and I pass a few N500 cars and a Gr.4 car, I'm not racing against them. Therefore if I bin it two corners later, it doesn't actually matter if they've despawned and I don't see them come back past me, and I don't need to know where, when or how they finish, they don't even need a fully aggressive racing AI. They literally just need to be track furniture. Yeah, it's not 100% real, but it's more real than doing 10 laps of the Nordschleife and only seeing 1 other car. Perhaps in a GT500/GT300 race at Suzuka the inconsistency of the positions would be more noticeable, but again, I think it would feel like a net gain.