Sorry for late reply, so after that time, I then decided to reinstall Windows and then do various testing including using my phone as hotspot relay (my phone connected to the router 5Ghz band, then I wireless tether it to my laptop using my phone 5Ghz band).
My conclusion is, either the driver or the Intel AX200 in my laptop have bugs/problem communicating with my router (Tenda AC6). Why? Because the hotspot relay had full speed instead of limited speed. I tested this next to the router itself so signal strength wasn't a problem.
I'll post the screenshot soon after I removed sensitive information from it.
https://imgur.com/a/iw3hGuB
Other than replacing my routers or using my phone as hotspot relay, I have no other choice, I guess.