Hi Steve,
having the USE_MAXON_API being defined - actually using C4D=true in projectdefinition.txt - is required in order to be sure that all the cinema.framework classes are properly compiled. Although there could be situations where some cinema.framework classes can work without that define, we highly discourage this approach since you can end up in situations where the code compiles until you include that specific class which indeed needs that define (which it's already happening in that case).
If specifying C4D=true actually brings too much pain, please open a new thread and let's proactively discuss the issues your code is facing and let's get rid of them.
Best, Riccardo