I think the confusing nature of the arguments reflect the fact that the Scottish Govt are trying to use the Section 35 to force a court showdown with Westminster.
Nobody really cares about the effects of the GRR Bill, and haven't even really given them much consideration. Bain has outsourced her arguments from Stonewall, a lobby group.
The GRR Bill in this instance is a McGuffin. A plot device.
What they didn't think through is the ridiculous assertion that this only impacts on trans people, omitting that changing the definition of sex affects absolutely everyone.