It is critical to have a missing dimension "HCM - Workforce Core"."Hierarchies"."Assignment Manager List"."Manager User Name".

Yes, the Subject Area has the one:

"HCM - Workforce Core"."Worker"."Manager Information"."Manager User Name"

that's not enough, it returns only direct assignment manager-employee list.

When the user is querying managers that has the other managers as their employees, the user has to use "HCM - Workforce Core"."Hierarchies"."Assignment Manager List" to get full list of the employees to the bottom. If we want to filter the result for the current User ONLY, we have to join it by the USER() function to the "HCM - Workforce Core"."Hierarchies"."Assignment Manager List" and the "Manager User Name" is not there.

The problem seams so obvious, I created this idea before filing SR as a BUG to get the community feedback.