Laurel's problem is that until she's Black Canary she has no purpose, other than being Oliver's ex. They seemed about to make her a Harvey Dent character in season 2 (DA working with Arrow and the cops), thereby giving her an actual place in the show, but haven't followed up on it at all. They've tried giving her other plotlines, but all they've done is led to inconsistent characterization (the addict thing).