The scoring problem has nothing to do with the passing game
Overall, the Steelers are tied for 22nd in the NFL in total TDs scored this season (36), but that's not a reflection of inefficiency in the passing game. Despite the backup QBs combining for one whole TD pass in the three-and-a-half games that Ben Roethlisberger didn't play, the Steelers tied for 8th in TD passes this season (27). It's everything else that's the problem. The Steelers tied for 27th in TD runs (8.), tied for 25th in TDs scored by the defense (1), and tied for dead last in TDs scored by the special teams (0). Simply put, the Steelers were one of the 10 best teams in the NFL at scoring TDs through the air, but one of the 10 worst teams in the NFL at scoring TDs on the ground, by defense and by special teams. The passing game was not the problem this season.
By the way, if Roethlisberger played all 16 games this season and threw 33 TD passes as I determined he would at the pace he was throwing them, the Steelers would have ranked 5th in TD passes, and tied for 15th in total TDs if the scoring output from the running game, defense and special teams remained the same.