The problem with that argument is that, IIRC, there is direct evidence that one reasons that the abuse was covered up was that authorities were afraid of being accused of racism and/or of stirring up ethnic tensions. I don't think that, to accept this, you need believe that CPS is always perfect when this issue is absent.

This is one of the factors that lead to crimes not being better investigated at the time, but then fear of tensions would cases where the alleged perpetrators were white and the victims/witnesses non-white as in the OP's question. (And more generally, teenage girls from working class backgrounds got far less sympathy and far more scepticism than they should have done from the police and CPS and even social workers when they talked about being sexually exploited regardless of race. Certainly no evidence was found they were much more keen to listen to non-white victims or prosecute white people...)