Second part I have never noticed. Just loaded into patrol to check and holding does give some extra height, not much but 10-15%? I'm on my warlock atm so can't do proper testing when using holding as possible help for hunter jumping, but at least for warlock glide whole holding jump down thing seems useless. Also I have done KF jumping parts as hunter couple times now, never knew about or used holding X as help :b
Also if jumping button didn't return value to 0 after initiating jump you would keep jumping up and down 24/7 on the ground when holding X down.