Are you referring to your Windows system?
Okay, if it is possible I would like to determine if the issue is related to downstream side of the ASUS or the upstream. To accomplish this you will need a pingable device connected to the Ethernet LAN of the ASUS. Now perform the following:
- Using the pingable device on the Ethernet, ping 8.8.8.8 or your ISP gateway. Note the results.
- If possible, ping that device from another device on the Ethernet LAN of the ASUS. Note the results.
- Ping one device on WiFi from a device on WiFi. Note the results.
Based on your "50mbps and 150mbps" on the Ethernet connection and "250" on WiFi, I would expect ping response times WiFi to WiFi to be equal to or even faster than Ethernet to Ethernet. And all the local pings to be faster than the ping to 8.8.8.8 . This would indicate a router issue; hardware, firmware, or configuration.
I am suspecting something associated with the modem connection to the ASUS, if Ethernet to Ethernet ping is faster than WiFi to WiFi and pinging 8.8.8.8 is slower compared to WiFi to WiFi.
Does the ASUS indicate a physical connection of 1Gbps to your ISP modem?