I’ve been getting around this by doing a sort of light based AO. Using a 200 white override mat with AO enabled on the GI tab, set to a very high value like 5 feet or 10 feet. (Giving the whole scene some elements of AO.) Then comping in post, works quite well.
I still struggle to get those darks and mids with the normal renderer. We tried using a lot white base value such as 153 but it all broken down once we started loading textures in. Getting the junior artists to clamp the texture colors turned out to be harder than expected.