I'm not saying he's clutch, I'm saying his style of play doesn't preclude him from being clutch. That said, in the limited sample size of playoff games he had, he did nothing that would worry me. If anything, his mini run in Tampa was somewhat impressive, definitely on the "good" side more than the "bad".
As for your last question, he's worthy of a roster spot because he showed he could be one of the most offensively dominant player on the team for stretches that were long enough not to be a fluke, on top of his visible, visually obvious talent. He's 25 years old and scored 50 pts twice already, which were considered to be "underwhelming" for him; that should tell us about how people perceive his talent. Injuries and his mysterious leave of absence destroyed any momentum the last two seasons; as far as I'm concerned I just check them out and look forward in his case. Hopefully he can finally put it all together in a complete season.
Those are the main reasons why he would deserves a Top 9 LW spot, and quite easily so. The last season he played that wasn't screwed by injuries or leave of absence, he scored 53 pts. Not great but not bad for a Top 6 LWer.