Hierarchy on navigational attribute decreased query performance

A multiprovider, based upon 5 different infoproviders and 2 infoobjects, was causing a performance drain whenever a query was executed.
Every query, based upon this multiprovider, contained a hierarchy on a navigational attribute of an infoobject.
Eg. Infoobject A --> navigational attribute B --> Hierarchy C.
To make sure that the hierarchy was displayed correctly, also infoobject B was added to the multiprovider, eventhough this had no added value (as no "fact" data was to be displayed which "belongs" to infoobject B)
Infoobject B (IOB in the picture below) is a navigational attribute of 0MATERIAL

Infoobject B (IOB) has been added to the multiprovider and was identified (assigned) via the checkbox.
After the checkbox was "un-ticked" (as seen in the picture above; red arrow) and thus infoobject B was no longer part of the identification, the query performance increased.
Conclusion: Know what you're doing when inserting infoobjects in a multiprovider as mis-usage can drastically decrease performance!