Poor speed

I reciently purchased a Nighthawk MR60 Mesh system to replace an older Orbi Mesh, and the speed has dropped considerably. I have GB service through Xfinity, with a GB modem. I currently have 1 MR60 router, and 4 satelites spread throughout my 5000 sq ft house. The speed at the modem measures about 800 Mbps, but through the mesh system I am getting only 65 Mbps. Where is the speed going? I have 14 devices attached. Is there a faster or more robust mesh system available???