The defense did okay on Sunday. Generally, when you hold a team to 16 points you win the game. Unfortunately for us, that presumes you have an average offense. The average NFL offense scored almost 20 points per game in 2018. Right now, the Denver Broncos have a below average offense.
In order for Denver’s defense to work, they need to be able to stop the run on first down. The Broncos were okay at that against the Oakland Raiders (48 yards on 14 first down carries - 3.4 ypc), but not so good against Chicago (89 yards on 15 first down carries - 5.