I have some more info now. I just set the upload / download in QoS to 1000 MBit both. Ignore the rest. Enabled QoS and got the same result as above (full upload, about 33% download). I then rebooted...

I have just upgraded internet from FTTC to FTTP. Setup the router to Wireless Router Mode - and everything connects correctly. My provider offers 500mb down, 70mb up. I have no issues with download...