Hi Andrey, Ishan,
thank you for your responses.
I agree implementation of a global report suite in combination with virtual report suites that split up the data is the right approach.
Something we have positive experience with multiple clients.
This was a one-off where the merge is requested post-implementation - we'll look into both options. Either Rollups with the mentioned disadvantages or indeed changing the implementation.
TLD;r Global report suite with split-up per virtual report suite is the way to go.