The 49ers averaged the second-most rush yards per game of any NFL team during the regular season, and were tied with the Minnesota Vikings for the fifth-most sacks in the league. That's what you call "complementary football."
By running the ball well, the 49ers routinely shortened the game and inherently put their opponent in obvious passing situations. With a dominant defensive line, that consistently played right into San Francisco's hands.
The eye test was proof enough, but the stats back it up, too. In terms of net passing yards allowed, the 49ers just produced the most dominant defensive season in a decade.
#49ers allowed 169.2 net yards passing per game this season fewest in NFL since Jets allowed 153.7 in 2009— Josh Dubow (@JoshDubowAP) December 30, 2019
Net passing yards subtract yards lost due to sacks from a passer's total yardage. So, each of San Francisco's 48 sacks on the season impacted that per-game average. Considering the NFL has become a much more passing-friendly league in recent years as a result of rule changes, the 49ers' ability to limit opposing passing offenses is all the more impressive.