So, when I have been testing, it has been in various ways with the same results.
So I have tested with the Hub in router mode with Ethernet only, then Wifi Only, then while both in use. All achieving similar results (much slower download speeds on wifi of course)
I then went out and bought a Nighthawk X6 R8000 which we now use as the Router with the Hub 3 in modem mode.
I have run the same speed tests as before using both Speedtest net & think broadband. Same results, upload speeds very inconsistent but download speeds always 80% and above.
The router also has its own built in speedtest feature which picks up the speed it receives directly from the modem... still shows awful upload speeds majority of the time.
Majority of the tests were done through my desktop PC or a laptop both connected via Cat 6 or Cat 7 ethernet cable (swapped and changed to ensure the cable wasn't faulty)