Well I have come to realize that after more testing, it was not the ipv4 or ipv6 issue. I found that sometimes (tm) it will download at maximum speeds while connected in bridge mode.
Additionally another update, I am seeing similar download issues from other Google downloads. Specifically, I am seeing the same slow download speeds from the Nexus and Pixel images which also, as you may guess, have an increase in download speed while uploading.
@m1dy
Can you try downloading an image from there and see if you get slow speeds as well? I found that Chrome downloads are 10mbps but with parallel streams, I get 100mbps without any uploading. Uploading brings me to over ~500mbps.