While I agree we didn't see Brassard playing to his potential for most of his time in Columbus, I think the Jackets would still have zero playoff appearances if it wasn't for Brassard and his line coming strong out of the gate in 2008-09. It was the general consensus at the time that his line was the strongest, and he the strongest on it, for the first 20 games or so, while others were still trying to remember the season had started. His play dropped before he was injured, that being said. I'm certainly not saying he was the biggest reason the Jackets made the playoffs that season, as Nash decided to step up his game, but he did his part to make it happen.
I do think it's likely Brassard will remain the up-and-down player for the Rangers that he was for the Jackets. If so, that's just the player he is. Not everyone is a Sakic or Yzerman, despite what you hear every draft.