How to merge data from multiple reports?

I have been tasked with reporting on email utilization per employee. I know there is a built-in Excange Online connector and I've created a basic report with it using my own mailbox. (It's incredibly slow due to email volume but that's a separate issue.)

This connector will do what I need on an individual level but it means every employee needs to run the report with their own credentials! We're a small company so that might be doable. But even if I do have staff do that, how do I aggregate all that data into another report while simultaneously keeping each individual's report private except to management? If staff publish their reports to a Workspace, that would mean everyone would have access to the datasets and reports there, right?

Please help me solve this technical problem.