all the descriptions of the fossils/bones seem to uphold a null hypothesis of: there is no significant difference between these and modern waterfowl bones.
Nope, reading the actual journal article they place Gansus basal to Carinatae and Neornithes, the clade of all modern birds. I don't know enough about bird skeletal structure to determine the differences, but they must be notable for it to be so far removed. It seems the key differences eliminating these from Carinitae and modern birds are the bony structures of the limbs.
Really?
I take you have a full description of all fossils including the diagnostics?
Feel free to post it here.