The tension struts are not the only structural attachments for the MRGB. There are usually other attachments at the base of the housing. The tension struts connecting the collar at the top of the housing to the airframe are mainly used to minimize bending/distortion in the housing due to out-of-plane rotor mast moments, but they also take vertical rotor lift forces. Attachments at the housing base perimeter are used to handle in-plane rotor moments.
The tension strut arrangement is more weight efficient since it allows the housing structure to be made much lighter. Isolating the housing structure from most of the bending it would normally experience significantly reduces misalignment of gear meshes and rolling element bearing contacts.
Here is a nice photo of the tension strut and collar attachment on the H160 MRGB.