I think it's understandable why they do that in WoW, since it's a new expansion so they gotta make the players feel the progression. To make players sink their souls more into the game. ($$$ kaching!)

But in this case, in D3, is just silly lol. The white crossbow that deals a lot more damage, has a level req of 55 and the legendary's 56, but deals a lot less damage.

That's the exact opposite of progress

Oh wait you're right, the quiver should add some DPS too