Why does Rek'sai not have shared cooldowns?

She's another "Form shifter" in a way that by burrowing, she gets a new skill-set to depend on, and I'm okay with that, I'm just rather annoyed that Jayce, Elise, Gnar, Nidalee, and now Rek'sai all have seperate cooldowns when they switch between their two forms, yet Quinn is the only champion that has completely shared cooldowns on both her human and bird form, why?

I'm also finding it ironic that the champions who do have separate abilities are all fairly balanced, maybe with the exception of Gnar, yet Quinn is sub par and really only a champion you should pick if you enjoy her as a character, not as a chance for winning. The only thing she excels at is basically assassinating the ADC with her ultimate, but she relies on a slow skillshot to duel in human form, which isn't hard to hit, it's just rather easy to dodge. The league has only a few ADC's that are commonplace because they simply out perform the others. About 85% of the ADC population played is probably made of five to six champions, no?

Either way, Quinn's in a bad spot and you've recognized it, yet you still made another champion that doesn't even really fit the shapeshifter category and yet has separate cooldowns.

P.S. Don't get me wrong, I've won quite a bit of games with Quinn, but I've only ever played against half a dozen in a few months? She's so underplayed because she requires more of an assassin like play type with her ultimate without the survivability complex. She's a, if you find the adc alone or if the mid lane isn't a burst caster, go for it, but only if they're alone. Her entire kit is dependent on "1v1 me m8" but the fact is, teamfights usually start at 15 minutes or so now.