Sawyer is unique in that he survives through all 6 seasons, while never getting to do something truly important.
I'm specifically discussing how important each character is to the progression of the story. It's not about how much fans like the characters, or how much screen time they have.
The "big five" -- Desmond, Locke, Jack, Hurley and Ben. All five of them have important purposes in the story. Main events don't happen without them.
And then we have Charles Widmore, Richard, Jacob and MIB who are also important to the story.
I would argue Kate and Faraday are also more important than Sawyer. Kate because she is a female protagonist and a top billing star on the show. Daniel Faraday because he's responsible for explaining the time travel mechanic to other characters, and to the audience.
Sadly, that leaves Sawyer out of the top 10.
Sawyer has always been someone who's kinda just there, rolling with the madness, surviving. He caused some events and assisted in some other events. But he's never a central or leading force.