Hi,

This is what i have,

Time 500mbps
router: TP-Link c1200
modem: Huawei EchoLife HG8240H

Laptop: Intel® Dual Band Wireless-AC 8265 (2 x 2)
PC: TP-Link Archer T4U USB Wifi Adapter (2 antenna and support MU-MIMO, 2x2 correct me if im wrong) connected to USB3 port
phone: note 9 ("enhanced 4 x 4")

all support 802.11ac and i connect my devices to the 5ghz band.
speedtest using a few different tools such as ookla speedtest all gave me similar results pretty consistently.
DL: ~250mbps  UL: 300 - 400mbps
all settings at default/auto

Also tried manually configured afew things as suggested above such as setting channel width to 80mhz, change channel and so on

if i specify cahnnel width to 20Mhz, the speed does go down, so it indeed affect the speed.
after changed to 20mhz: DL: ~150mbps  UL: ~90mbps

Am i missing anything? (i actually created ticket to Time to ask for technician to check, pending respond)

may i know which router?

not cheap, may be later find one cheaper one aha
I tested lan cable can go up to 450mbps(is that normal? thought it should near 500 like 480+), so like what you said, really the router wifi capability cannot la. Today testa bit better, able to get up to 300mbps depending on the server i chose.
later got budget change to a better router.