She was supposed to the Black Canary since the beginning right ? So basically her arc in s1 consisted of being the main love interest stuck in a love triangle and the moral civilian anchor through her being a dedicated and commited brillant lawyer.
During s2 she spiraled down due to Tommy's death and climb into the bottle. However, I always wondered, as Tommy was not supposed to be killed at the end of s1 how would her arc been ? Because they literally killed Tommy to make Oliver's journey evolve but also hers.
After they decided to bring Sara in who is a skilled talented fighter and an incredible Black Canary. Her history with Oliver and her own history on Lian Yu is huge and she became the female fighter BC pairing with Oliver. She was the best BC that the show ever had to finally replace her next season with by her sister who took on the mantle because she got murdered.
They waited 3 seasons + they brought a (better) Black Canary in between to finally make her become the Black Canary.
And so I guess that the only rason Sara was killed was for Laurel to take on the mantle right ? I mean they replaced Sara who was the besr BC (imo) with Laurel who obviously was less skilled (and it's totally normal given the storylines then).
Not to mention that initally the show was supposed to only last for 5 seasons so her journey to become the Black Canary was really late for someone who was always supposed to become the Black Canary no ?
Laurel working as the CNRI during s1 was great as she really represent the moral civilian anchor of Star City ready to push boundaries. A hero without mask. Maybe the should have kept going in that direction at one point. It's only my opinion of course.