Kha'Zix was already incredibly strong before this 'compensation' for the Duskblade nerfs (which he could abuse so much harder than anyone else)
Now with this serious overbuff, with the logic behind it being that they removed an effect on his W that most players didnt even know he had, that he shouldn't have had anyway, for an extra .4 ad on Q.
Kha'Zix still builds Duskblade. He still abuses it. Now hes even more top of the jungle.
EDIT: The buff is actually way bigger than .4 AD. ORiginally he ha 120% AD and 65% isolation bonus, now its 130% (which should be enough by itself) and 100% bonus. So thats actuallly .62% bonus ad increased for no reason. Remember wukong buff? Scaling added per level? Nah fuck that we gonna give an extra .6 at base.