As per our understanding from the scenario mentioned above, The solution proposed by you will work appropriately and the Report Suite "C" will serve as Global Report Suite . Some of the benefits / points of consideration for using Global Report Suite are-
De-Duplication: Global report suites de-duplicate unique visitors. For example, if a user visits three of your domains in the same day, Global report suites would record one unique visitor.
Time frame: Global report suites report data with standard latency.
Breadth: Global report suites can attribute credit to conversion variables between report suites, as well as provide pathing across report suites.
Historical data: Global report suites only report data from the point they were implemented.
Reports: Global report suites provide additional information on ALL reports implemented.
Global report suites can be used across all products, and can have an unlimited number of child report suites.
Please let us know if you have any more questions or queries.