Thank you for the great information. Let me propose that we use your ROG Asus laptop as a test tool. Additionally, let's use
http://speedtest.xfinity.com to test speed. For me, I get the same results whether I am attached to Ethernet or WiFi. Now let me propose test scenarios:
- Remove the Ethernet cable from the WAN port of the ASUS router and plug it into the laptop. Run the speed test. Report results. (I expect that even with WiFi enabled on the laptop, the laptop's routing table would choose the Ethernet as the preferred route.)
- Re-attach the Ethernet cable to the WAN port of the ASUS router. Using a different cable, attach laptop to a LAN port of the ASUS router. Run the speed test. Report the results.
- Remove Ethernet cable from laptop and connect laptop WiFi to ASUS router. Run the speed test. Report the results.
For me, running the three steps with my ASUS RT-AC86U, the results were almost identical. Based on what you have reported, I would expect that your results for step 2 to be significantly less than steps 1 and 3. If this is the case then perform a factory reset to your ASUS RT-AC86U and reconfigure. DO NOT CONFIGURE ANY FEATURES. Configure enough to restore WAN and WiFi connections. Repeat steps 2 and 3. Report results.