i understand wireless is not a reliable but i have been doing this tests in similar fashions and i consistently get the speed tests i mentioned.
As for running these tests i do not see the red light for high traffic prioritization.
As for qos not working cause i dont have anti bufferbloat set to always i am not convinced that is true because when changing bandwidth distribution i noticed the numbers would on speed test would change.
I have updated the firmware and have not done a factory reset i will do that to see if it helps and perfom wired speed tests. Let you all know the outcom
QoS only works all the time when set to "Always" when 'High priority traffic is detected" it kicks in when you start gaming. I have mine set to "when high priority traffic is detected" so when I game my internet speeds drop to 70% of 55Mbps (I have my antibufferbloat set to different percentages but using 70% for simplicity here) so because its set to detect high priority traffic with the sliders at 70% I get 70% of my bandwidth which is 38Mbps. I can test this on my iMac and that's what it gets, if I adjust the QoS when gaming then it will change, so if I move the petal slider for my iMac to 25% then it will get more bandwidth (be aware you have to do this for both download and upload separately) if QoS was working all the time in "high priority traffic" mode you would be seeing the percentages in QoS all the time that are linked to the antibufferbloat settings, which for you is 70% of your total bandwidth. Have a look at this video its a great explanation of QoS and antibufferbloat. I've set it to start at the part about antibufferbloat and QoS. https://youtu.be/KQiwtXoNqsA?t=37m40s
You did not answer about setting up with smart connect enabled or disabled? During the set up sequence you can split the bands to 2.4 and 5Ghz separately and have different SSID's for each band so you know what devices are using what. Also no matter what Wifi is not a good way to check speeds, and an ISP will always ask for a hardwired test if you are having issues for a reason... Let us know how you get on.