I have a RT-AC88U running 384.2_4 and while my upload speeds are only 12 Mbps, I’m getting that over wired.
My router only joins the mDNS broadcast group on br0 while yours does br0, br1 and br2. From reading it looks like br1 and br2 are either bridged or guest networks. Are your lan devices on a guest network or something that is configured as bandwidth limited?
Also it looks like you are running a bunch of custom scripts. Have you tried temporarily removing them?
And so I turned my live home network into a testbed lol... Please find the test as outlined below. Please let me know if anything was missed or is unclear. I thank you all in advance for taking a look at this, it's a lot of steps and logs. My family here have been grumbling the whole past hour or so while I was rebooting and stuff... In the end, the problem is still there. I fully reverted to pre-test state now (didn't do any restores). Please take your time. Cheers.
TEST SEQUENCE LOG:
TEST START:
Speedtest 95.56/0.92 (wired)
Speedtest 124.76/142.98 (wireless)
Disable "Enable JFFS custom scripts and configs"
Speedtest 94.47/0.88 (wired)
Save syslog(7).txt
https://pastebin.com/Jqg9Rvj7
Reboot
Save syslog(8).txt
https://pastebin.com/kdzxPtVL
Speedtest 92.32/1.05 (wired)
Speedtest 158.16/144.38 (wireless)
Disable "Enable DNS-based Filtering"
Speedtest 91.52/0.93 (wired)
Remove USB "Safely Remove disk"
Physically remove USB drive
Save syslog(9).txt
https://pastebin.com/ii8Ur0Zn
Reboot
Speedtest 93.31/0.88 (wired)
Remove Guest network 5GHz
Remove Guest network 2.4GHz
Speedtest 91.24/0.99 (wired)
Remove all lan port connections except local
Save syslog(10).txt
https://pastebin.com/pm1vrfRJ
Reboot
Save syslog(13).txt
https://pastebin.com/5nhwJzyE
Observed: br1 gone!
Speedtest 94.06/0.92 (wired)
Speedtest 155.44/148.45 (wireless)
PROBLEM PERSISTS!
Disabled QoS (previously Adaptive QoS/Automatic Setting)
Speedtest 93.20/1.03 (wired)
Speedtest 151.61/145.46 (wireless)
Save syslog(14).txt
https://pastebin.com/pKquLChx
Power off
Power on
Speedtest 92.52/0.86 (wired)
Speedtest 151.84/144.32 (wireless)
Enable QoS (Mistake! Syslog should've been taken first!)
Save syslog(15).txt
https://pastebin.com/UVQbVgvt
REVERT ALL STEPS ABOVE!
Speedtest 89.86/1.08 (wired)
Speedtest 129.56/123.83 (wireless)
PROBLEM PERSISTS!