Yes because its fair for a class who builds full damage and has limited defensive options to do the least amount of damage for the entire game because some arbitrary idea on the boards that says a full damage, fed carry who is being buffed and aided by a support should not do damage to squishy targets.
Furthermore, they aren't adding more damage. Where do you see more damage added? ADCs can get 100% crit now and guess what? They still do shit for damage. The only change I see that would give more damage is IE. That's it. The other changes on the table reduce the amount of crit ADCs get from each item(there by reducing the gold efficiency of those items since the price is not going down; furthermore, the energized attacks are getting changed from a scaling amount to just a flat 80 magic damage. Wow so much additional damage, especially when considering at max level it could do double that) and a change to PD that while, yes, it is getting 20 AD, is also now going to be a defensive item that doesn't put ADCs in a trough for going for a defensive option first. So they're on the same wave length item wise with mages; how terrible, being able to build a hexdrinker into a double mage bot and survive. Its not like Mages can't first build Seekers and sit on it without losing damage. Its not like Assassins can't first build hexdrinker and sit on it without losing damage.
And the IE change, one option would be to make the fucking thing 5k gold. No other class would have to wait 5k gold just to get their first item powerspike. And for 5k gold, it better give good fucking stats.