there is a lot of damage reduction on those new items for adc. 12% on phantom dancers, then the damage delay on whatsitsname, and this mastery.
thow
at the side of an adc for shits and giggles to watch him turn into a better tank than actual tanks.
being squishy is absolutely the only disadvantage adc have right now. they have high damage, high amounts of cc a lot of them have mobility and some of them burst. and then there is that one who has all of that in 1 kit 
but wait no. giving %damage reduction to adc on their core items instead of tanks is apparantly ot enough. they also have to have 70% to 100% crit lategame by buying the same items as before, a stronger early game, relative cost decrease on all their items to create a stronger midgame, and the ability to stack massive amounts of lifesteal.
this is going to be the worst patch in the history of this game.