He's not a QB to "carry" the team and not many do anyway, that's overblown, they all need help. Think Brady wins the SB without that D and run game?
Remains to be seen what this offense will look like under Young Kellen and if Dak has improved in the off season under real game circumstances.
As far as doubts, I don't have them that he can't manage the game and execute the offense and provide a little extra oomph with his legs because I do not fault him for not advancing in the playoffs, that's on the D as it has always been even with Romo.
The real problem, the real doubt I have is with this D, not Dak, with or without Elliott. We're really good at selling ourselves that we're finally getting there and we never quite do.