Oh I have a question on lifesteal items. It's pretty noteworthy that both BT and Shieldbow start scaling later into the game, which I assume was intentional. Were there specific reasons you wanted lifesteal on adcs to be less prevalent or nonexistent before 3rd item or so?
Shieldbow is more important here where if you give a champion sustain + damage + burst resistance exactly what are you meant to do to them? The item does literally everything. This is mostly a problem in the early game where one champion can't really hope to burst through a Shieldbow.
Bloodthirster is less important here but sustain is still a pretty scary stat to give early game. If BT is meant to be a satisfying life steal item, it makes many lanes completely uninteractive. You get to side step those issues by telling players "Look, this item is good, but you have to buy it later."