It appears that Rangers attack speed isn't actually being 'doubled' right now. Instead It's adding 0.7 * 0.7 to their attack speed. So Rangers start with 0.7 attack speed, then when 'doubled' they have 1.19 attack speed ( 0.7 * 0.7 + 0.7). Essentially instead of actually doubling their attack speed Rangers are getting 70% attack speed increase.
See linked image for Vayne with the 'doubled' attack speed.
borbes1 votesWorking as intended. All multipliers are additive. It adds 100%, so with a Recurve it would be 120% added (.7 + .7*1.2 = 1.54 attacks per second). Tooltip could be better. Attack speed hard cap is 2.5.
OrderChaos1 votesThis isn't with any items involved. A 'doubling' implies increasing attack speed by 100%. 100% of .7 is .7. Attack speed is not being increased by .7, but by .51 or 70% of .7
Using your same formula without the recurve, 100% added would be .7 + .7*1 = 1.4 attacks per second, not the 1.21 it's giving.