They improved the front line too.
There is little doubt that more intense completion at cornerback, defensive end, defensive tackle, left guard, left tackle and wide receiver has enhanced overall performance.
Some of the incumbents at those positions were coming off disappointing seasons. Some of them needed their buttons pushed, and nothing does that better than the hot breath of competition on your neck.
Bears players have been less secure than in recent seasons. Thus, most of the returning players have had to re-earn their scholarships.
Tim Jennings might not have four interceptions if not for Kelvin Hayden. Israel Idonije and Corey Wootton might not have four sacks between them if not for first-round draft pick Shea McClellin. And Stephen Paea might not be playing so well if not for Amobi Okoye and Nate Collins.
Even if Hayden never makes a big play for the Bears, he has made them a better team.
Jennings, who might be the team's most valuable player through three games, got a jolt when the Bears signed Hayden. He had been a Colts teammate of Hayden's for four years, and Hayden was usually ahead of him on the Colts' depth chart.
"I knew I had to step up my level of play to stay where I was with the team," said Jennings, who was benched late last season. "I know he's a starter in this league with any other team, so I had to prove I was a starter also and make the coaching staff make a tough decision."
Jennings acknowledges Hayden's presence made him rededicate himself.
"I can say that he made me work harder," he said. "I had to stay on my toes all through the OTAs and training camp. They added him for a reason, that's the way I took it."
Idonije was in a little different situation. He is used to having competition nipping at his cleats. He came into the NFL as an undrafted player and has had to ward off competition virtually ever since. That's why he approaches his job with a free agent mentality, saying he is "intrinsically driven."
But after a down year in 2011, he acknowledges he kicked it up a notch too.
"I definitely was more motivated this year because last year I left a lot of opportunities on the field," he said.
And if he were not more motivated, it is likely he would have lost more time to McClellin or Wootton.
Instead, Idonije has benefited from McClellin's presence because it has meant fewer snaps and fresher legs for the veteran. This has helped the pass rush overall.
Any veteran receiver who thought Alshon Jeffery was going to have a redshirt year has been in for a rude surprise — and perhaps a loss of playing time.
Nobody has had to look over their shoulder for Brandon Marshall because he came in at the front of the receiver pack. But he still has made other receivers better, and his pushing the envelope has made the entire team better.
Thirty minutes before practice starts, Marshall is out on the field preparing. In camp he was doing cone drills, working the jugs machine, doing ladders. And he isn't giving Bears defensive backs the brother-in-law treatment during practice.
"I watch Brandon, how hard he works," Jennings said. "Speaking with the guys, we all notice it. We picked up on it. That carries over through the whole team. Every guy has wanted to do extra because Brandon is out there doing it.
"When you have that kind of leadership and motivation, the sky is the limit. To see him doing the little things like that where he is in his career makes you want to elevate your game."
Bringing in a player like Marshall, who can force defensive adjustments and make big plays, is the ideal.
But bringing in a number of players who can raise the tide — and all the boats with it — is a pretty good thing too.