Perhaps you should use QOS to prioritise outgoing ACKs and maybe implement FQ-codel
As it was downstream congestion prioritising acknowledgements wouldn't really have helped, that only fixes upstream.
Changing queuing strategies wouldn't have really been helpful as all the significant traffic was single flow TCP and time insensitive, removing buffer bloat wouldn't have done much. My stream was getting a fair share of the downstream pipe, there were just too many other demands on it for that fair share to be adequate for my application.
My only real option would've been to either prioritise my own devices above others or to use something layer 7 aware that prioritises traffic from YouTube, etc, above other traffic or recognises XBoxOne downloads and deprioritises them. From the point of view of TCP they would all look pretty similar.