"biofemales"? You mean "FAAB"s, "female assigned at birth"s, right? o.O As for GI - it certainly does mix gender and sex. It also seems as though it needlessly pathologises especially boys who are not into boy-things. I think girls wearing boy-coded clothes and playing with boy-coded toys are less likely to get difficulties than boys playing with girl-coded toys or trying to dress in a way that's considered feminine. Tomboys seem to be a lot less threatening to gender standards than... is there even a term for "boys who are into 'girl things'" that's not a slur?

I think making the definition hinge on weight is deeply dangerous to treatment.
Oh god, yes. I don't know why they want to perpetuate the myth - and I think this certainly contributes to this - that these two conditions are primarily about the person's relation to their weight, that the weight somehow is the problem that needs to be addressed, rather than whatever caused this condition. It's not likely to be a lack of other dieting options.