Has this been fixed on the C7?
Had the same issue.
New C7 hub. Did not restore any backups, instead did a fresh setup. Using an Asus router and had assigned a static IP to the new C7 hub. Rebooted the hub multiple times but the sluggishness remained.
Followed what @bobbyD mentioned above. I went ahead and accessed HubIP/hub/advanced/network/lanautonegconfigenable and voila, the slowness disappeared. It saved me a hard reset and setting up everything again.