Did you look at those games:
Against the Browns, he got a last minute TD to win the game 16-13.
Against the Raiders, he got a last minute TD to win 13-10.
Against Indy, the Steelers did get the last points of the game, but with nearly ten minutes left in the game to win 24-17. It is a stretch to call that a game winning TD.
I just looked at his game log. Those are the only three games last year that the Steelers won by a TD or less where the Steelers scored last. If you want a QB who cannot score more than 13 or 16 points vs awful defenses like Cleveland and the Raiders, but can get a last minute TD; Kenny Pickett is your guy. Mac Jones might not have gotten those last minute TDs, but he probably wouldn't have needed them since the Pats would be already winning the games.
People on this board way overrate Pickett last minute TDs. A good QB wouldn't have needed a last minute TD against teams that scored 13, 10, or 17 points in a game.