The problem is we already have anti-assassin adcs, and would probably tempt Graves players into getting themselves into trouble when trying to fight. It also feels rather useless, as adcs tend to not want to get really close, thus you cannot really utilize his passive without getting into some degree of danger.
Which carry would you consider anti assassin?
Sivir (Spell Shield and Super Speed OP)
Urgot (Passive reduction of 15% all damage)
and Tristana (Knockback and Jump)
Sivir block the damage of a single spells, that's somethin which bothers neither talon nor akali.
Their gapcloser still brings them to sivir, even if the damage is absorbed.
Her ultimate sounds nice, but in the second you stop to attack the assassin you get blown up like every other ADC.
Urgot? Are you serious?
He's not even an ADC, but AD caster - and currently one of the worst picks ingame.
Regardless of his passive, if you pick Urgot as you "ADC" your team will loose post 25 minutes.
Urgot lacks everything which makes ADCs strong and allow them to win teamfights.
Steroids, range, mobility.
Tristana, well she can jump and blow assassins away.
These are nice tools which do help againsgt certain assasin (against those which are not invisible and need DPS to kill.)
I wouldn't call this anti assassin though, rather anti meele.
Oh no Sivir can't ultimately block the damage from 2 assassins from the 32 in game.
And who said you would try to stop and attack? Anti-assassins doesn't mean you kill them, it means you can survive them.
Urgot is listed as an adc, and whether he's one of the worst picks in game is opinion.
And whether or not you lose past 25 minutes is entirely reliant on how well one plays urgot and how well the enemy adc plays. You can't just assume a champion is a bad pick because he's non-meta, or lacks players who know how to use him well.
Tristana has the ability to knock people away and jump away, so I want you to tell me a single asssassin who doesn't need to get close to lay down his/her/it's burst. And she will always be able to use this, since all the assassins have had their silences removed.
EDIT: Also, your argument with Sivir is that the moment she turns around to fight she would die. Wouldn't that be the same issue with this graves passive you're proposing? He would lose the bonus armor and mr from it and only gain something he wouldn't be able to use before he dies.
