This isn't the 2019 Niners.
2021 Niners don't have a dominating D nor a top rushing attack. On top of that, it seems that opposing D's have figured out that Jimmy (be it skill and/or Kyle's play calling) thrives with short passes and a run game. D's are moving closer to the LOS and DARING Jim to pass it, and he can't...won't? Sunday Night, Green Bay's safeties were playing 10 yards from the LOS! That's just nuts.
Jim's yardage comes largely on the back of Kittle and the WR's who get YAC yards. The running game seems to be nonexistent even with an revamped line. Some has to be due to facing some good defensive fronts, but some is also due to the play calling. But what comes first, the play calling or the QB's skill? Kyle can't call plays that his QB can't make, so if you look at all the evidence you see tons of short throws and a few mid range throws up the middle of the field in the 10-15 yard range and barely any mid length tosses outside the hashes.
Until the passing game gets figured out and the D's are forced to respect it, I'm afraid the SF running game is going to have a rough time. I know if I was a Defensive coach playing SF, I'd be MAKING Jimmy G throw the ball 10+ yards downfield.