I don't think a TE is generally in a position to be the overall leader of a team, hell, Tony Gonzalez is probably the best of all-time, extremely hard worker, high character and this guy never won a playoff game until he was at the end of his career in Atlanta.
They just don't impact the game enough to lift up a team/teammates that are so deficient in other areas.
Some people say they wish we had a guy like Richard Sherman, well what do you think he'd be doing if Seattle didn't have a dominant pass rush and the best safety combination in the league behind him?
You think he could lift up a defense like what we had last year?
I'd love a player like that, but his impact is compounded by the fact that he has greatness surrounding him, he isn't lifting up a bunch of bullshit players or anything.
If Witten had been surrounded by a dominant OL/running game that would be one thing but I don't expect him to lift up an offense that has basically been just Romo slinging it around with a rotating number 1 WR until Bryant emerged, behind a shit OL with no running game and a novice coordinator running the whole show for the better part of a decade.