Short Version: Graves is everything Quinn is pretending to be.
Quinn is still Quinn. Basically the changes are when you vault Singed can't flip you immediately and Riven shouldn't be able to get a stun on you (though this is still to be tested myself). Other than that her Ultimate works slightly more intuitively considering you're not locked into the bird form as long now which gives you access to that very minor burst damage.
She was never unviable however, her passive can be a decent burst damage in trades if you actually want to get in range after Valor swoops down. However she is really comparable to Graves who basically is an identical champion with very similar skill kit and twice the burst.
Graves has mobility, a way to "blind" people from trading auto-attacks with him, an attack speed bonus, and a burst ultimate which is basically unavoidable if aimed correctly. Quinn has suicidal mobility, a less reliable way to blind opponents, her burst damage is nearly 100% RNG, the RNG gives her the attack speed bonus, and her ultimate has a 1 second delay on it to get the burst damage off (which does a fair bit less than Graves' instant version if there's only one target) meanwhile you're in a bird form that can't do anything but suicide in or run away.
When I play Quinn I feel like her Q needs to go through minions and explode at the targeted spot, or at the first champion it hits. I was really excited to use her after seeing the previews but everything is so underwhelming, and ulting feels like a tool purely for escaping or chasing.