I don't care if you think Draven's new Passive is "fine" or not. It's still a terrible Passive.
If you're snowballing, you're snowballing already, that crappy passive isn't going to do jack. If you're behind, that Passive isn't going to do a thing either because you aren't going to be activating that Passive with a Draven who is behind.
But let's ignore balance for a while and talk about satisfaction. Draven's Passive just plain feels terrible. His Passive makes Draven the first champion in LoL that gives the player a legitimate reason to rage at their ally for ks-ing. It actually makes getting ks feel really sh*tty because deep down you know the longer you hold onto all those stacks, the worst it will feel once you lose them, making your allied assassin a rival fighting over kills. It makes him completely incompatible with his own brother Darius
who is the king of kill stealing. Not to mention, you gave him his old overpowered Passive to show that he is Darius'
blood brother with his ability to make his opponent bleed just like Darius.
You succeeded in giving Draven a Passive that literally makes the player feel worse. Kill an opponent with little stacks built, then you feel pissed that you practically have no Passive. Die(which is easy for Draven to do) with a lot of stack built, and bang, all that time and hard work gone. You literally gave the player controlling Draven justification to rage at having his kill stolen because Assists means NOTHING to Draven.
It's not like other champions who build up stacks where their pay-off is often immediate and substantial. Or it's not like other similar Passives that also procs on minion kills or Assists.
Just adjust the rest of his kit if you really feel too afraid to give him a Passive that isn't disappointing. Take the time to adjust his numbers. Or think up something less infuriating. Give it an actual icon rather than a cropped image of Draven's portrait. The only people who genuinely likes his new Passive are those who do not like going up against Draven, or those who pretends to play Draven, but likes the whole "League of Draven" meme.