most of quinns problems could be solved by increasing her base ad/lvl
better synergy with items like
and
give her enough defense needed to be able to fight in valor form.
right now her base ad at level 18 is in the lower field of the champion pool, wich makes these items quite terrible on her. it sounds insignificant, but making them a more viable option would give her that little bit of a defensive boost that would make valor work a lot better in teamfights.
her early game might have to be tuned down so she doesnt turn even more into a lane bully, but im convinced that a buff to her base stats is all thats needed to make her work properly.
alternatively, just adding a % bonus to her base ad on her ult could work aswell. something like 10%, 20%, 30% base ad increase at rank 1/2/3 of her ult while she is in valor form.
this would end her up at ~130 base ad while she fights with valor.
its just about creating the right item synergy.