When lucian and Kassadin nerfs ?

They are, but not because they are inherently broken. The game just allows them to be.

In Lucian's case, the ADC rework allowed him to flourish because it become increasingly difficult to nurture any ADC that didn't build or . At that point, it was a matter of efficiency, though it didn't help that Riot buffed him when he was already sitting at a 50% win rate.

In Kassadin's case, someone figured out that since Fleet Footwork has redonk scaling with AP ratios, they could use this to negate his most glaring flaw - his lack of survivability. FF Kass embodies the passive strategies that Riot wants to phase out. They want you to engage with other players, not play farming simulator with minions.