Why have the assassins got nerfed?

What was the reason? Nearly all of them were unplayable (except mid lane Zed and jungle Rengar/Khazix maybe) in assassin role before.

Now akali, katarina, talon, shaco, leblanc, fizz are all nerfed into trash tier.

Riot thinks they need to give ADCs some time to react. But they didn't give the assassins the means to survive in that time interval.

Has Riot ever though that leblanc can live more than 1 second in team fights? Don't they know she just gets one shot when she is caught in a CC skill?

Why do Talon, Katarina, Akali, Rengar and Leblanc have much slower animations while using their skills?

Talon only snowballs if the lane opponent is stupid enough to let Talon proc his passive. Even if he snowballs, Talon will have a real problem approaching ADCs/squishy targets after mid game.

Katarina is Dravenized. She does have telegraphed movements in team fights. Also she is a squishy as well.