Ok, been tinkering with another device (intel nuc / mini pc) and tried installing OPNsense with internal ethernet (RTL8111) on WAN and the previously problematic usb to gigabit ethernet (RTL8153) as LAN. tried speedtest and downloads seems no problem which leads to more questions.
I know intel nuc and OPNsense is not a good comparison since comparing x86 vs arm and Linux vs BSD but I thought maybe there's more than just faulty usb ethernet. I plan to test it as openwrt in the nuc later.
Edit : after swapping the WAN side to USB Adapter and LAN to onboard NIC problem began to happens, and after further examination, previously the LAN side on my laptop is set to 100 mbps not 1 Gbps, maybe that explain why the USB ethernet works fine (similar when plugged in to USB 2.0 port). I guess it's confirmed the generic USB Gigabit adapter is very unrealiable that archieving 1 Gbps is almost impossible.