> My point is that it is also possible to make a clean room reimplimentation that is not a derivative work,

You have not at all established this point. What makes you think that the API of a reverse engineered implementation is not tainted by the copyright of the original API? It's clear that clean room reverse engineering produces an independent implementation, but it also seems clear that such a technique does not prevent the structure, sequence and organization of the original API from strongly influencing the structure, sequence and organization of the reimplementation's API.