Depends on your genetics. Bear in mind you have two parents, so there's also a 50% chance you'll inherit your hairiness from your mother's family.
I think some leg hair sparseness may be due to trousers rubbing, but some of it could be genetic. My elder brother & I both have hairy legs apart from the backs of our calves; my ex has hairy
everything. We all wear the same kind of stuff.
I'm now almost 2 years on T and my body hair is still developing. My abdomen, chest, shoulders, arms, thighs and back are now much hairier than they used to be, and whilst I too am blond the hairs have thickened and darkened over the years. On average, those hairs are about 20-30mm in length, particularly on my belly.
I'm also on the autism spectrum and I can tell you that whilst the extra hairiness feels weird at first, you do get used to it, and the same is true with facial hair. It's kinda like wearing a ring: at first it feels odd & a bit irritating to wear a ring on your finger, but then it just becomes a part of you.
I have to say, body hair is a wonderful thing. I sometimes find myself sitting & stroking my belly hair, like Blofeld but without the cat.