Shadow Assassin still inferior to Rhast
Rhast does better lategame with higher win rate too. So far playing Shadow Assassin 4 times in a row makes you realize that you could have pulled off those kills a lot easier with Zed. Then you play another game with Rhast and carry the game by yourself doe to broken lifesteal.
Its not a matter of nerfing Rhast either, since SA is so useless that nerfing Rhast pretty much means no one will play Kayn anymore.
The problem here is that SA wasn't buffed in the correct manner. I would say hes buff was a freaking joke. He clearly needs to do something better or Different than other champions like Zed or Kha zix, that currently do his exact job and so much easier.