Our closureCache at Types is implemented using our List:

private Map<Type,List<Type>> closureCache = new HashMap<>();

so there is a map from a type to a sorted list of types. I think that a linked list is not the best data structure to implement a list that should be sorted. Depending on the use cases a balanced tree, a plain java.util.ArrayList or a heap should be way better. I agree that if there is no performance slowdown, comparing the current implementation with all the alternatives, we can keep the implementation as it is.