First, the bad news: the team with the best QB wins; Mahomes > Allen; Mahomes > Jackson; Mahomes > Purdy. Even if Picket develops into a good too great QB, or the Steelers find another QB, the chances he will out play Mahomes are not good. He is truly the new Goat.
Good news: while defense and running the football will not win championships, they do give you a chance if you are good at it and get competent QB play. The Niners could have won the game. Take away the missed xtra point and the poor offensive execution on the last drive in regulation that resulted in the FG and left too much time on the clock, and they did have a chance.
In other words, I do think the Steelers could develop a team similar to the Niners by continuing to improve the defense, being physical and running the ball and getting competent and clutch QB play. Of course, they most likely will have to beat Mahomes.