I have also seen this behavior with the Vive Wireless over thunderbolt 3 on a laptop. CPU usage is usually high, but it drops frames and resolution (I assume to the minimum allowed) to maintain performance.
Razer blade Pro i7/GTX 1080 in performance mode (slight OC) with a Razer Core V1 (4 TB3 PCI lanes)
Issue not present on similar desktop with wireless.