FTTC connection finally fixed today, so had a go at getting this working again. I deleted the kmod-usb-net-asix package and then re-installed the latest version (and I’m on v4.2.3 of the router firmware) and as you can see from the screenshot, I’ve now got roughly the same amount of data received on each interface again.
And there was me thinking that as a vapid, air-headed, valley-girl, over his head, mouth-breathing consumer it was going to be beyond me to figure it out 
Lucky I don’t pay too much attention to 
Let me know how you get on!