Netgear R6080 AC1000 Router throttling internet speeds to 100Mbps

You've got a 400Mbps fire hose from your modem to the Internet and a 700Mbps fire hose from your router to your wireless clients, but you've only got a 100Mbps drinking straw between the modem and the router. That drinking straw in between can't keep either fire hose full. Upgrade to a router with gigabit Ethernet.

The internet comes from your modem with 400Mbit/s and goes in through the WAN port of your router which is a 100Mbit/s port. This limits the rest of the path to your client to 100Mbit/s max speed.

That the WiFi hardware in the router is capable of up to 700Mbit/s speeds can still make sense though, you can utilize those speeds on your LAN, internally, you just cannot get Internet speeds in excess of 100Mbit/s because of the limitations on the WAN port.