Assassin update question

I'm just curious about the assassin "update/nerf/rework/whatever this is it's still weird to me". So I'm hearing they're changing their ".25 second kill burst to about a 1 second kill burst". When, people like Veigar at full build can q and w and probably not even have to ult and kill in far less time than an assassin. Why rework assassins when there's plenty of champs like attack speed AP Teemo, stacked Nasus, stacked Veigar, not even full build Jax, Zed. Who can kill within a second. It seems the rework is only affecting some assassins. Will other assassins like the ones above be fixed too? Because I just recently picked up Rengar because of his auto attack based kit. (Which from what I see, is no longer gonna be auto attack based at all because his q is now more like a sweep into jab which you probably can't activate twice now, as any Rengar knows the get 4 stacks of ferocity then q and q again, probably will no longer work based on Riot's wording of this whole rework of his kit). I'm not trying to seem like I'm complaining or whatever, but I don't see a point to changing some aspects to some assassins when some other champions can kill FAR faster.