The old Quinn's issue literally was that her kit was not fit for the adc role. In bird form she was required to dive in the fray. And her passive being entirely random was a big no go for players that require precise actions to be performed.
The rework barely even fix all that. She was thrown in the ''ADC rework'' bundle because she needed it, but revamping her entirely would have taken its toll on her identity. And they wanted every champ to ''feel unique'' so they gave Quinn a "Unique'' mobility ulti.
She is still in a, strict way, a marksman. More now than before. But her kit is just unreliable. I see her fit the jungle playstyle more than the AD carry one.