Wi-Fi from the gateway is super fast but Wi-Fi speeds from router are 1/3rd the speed

I have the KVD21 gateway (1.00.16) and the Wi-Fi speeds are great. 500Mbps on average and as high as 700Mbps. But when I connect either of my new routers (ASUS AC68U and TP Link Archer A20) the Wi-Fi speeds never get above 200Mbps. No QOS or anything running on the routers. My cables are all high quality cat6. Any ideas?