Chicago Bears
The 2020 version of the Chicago Bears offense was a bit mystifying because although the Bears added veteran quarterback Nick Foles, the team retained former starting quarterback Mitch Trubisky. In essence, the Bears strategy was to trade a compensatory fourth round pick in the 2020 NFL Draft for Foles.
Los Angeles Rams
While Foles did indeed have a Super Bowl winning pedigree from his second go-round with the Philadelphia Eagles, his NFL career was a series of promotions and demotions as he has fought to earn and retain a starting spot on any of his five NFL teams. Unfortunately, his worst season occured when he played for the Saint Louis Rams in 2015. That did eventually lead to the Rams drafting rookie quarterback Jared Goff.
In 2020, the Bears did not have much continuity on offense. Trubisky played 10 games, starting nine. Foles played in 9 games, starting seven. While the Bears did have a solid running game when David Montgomery took the field, the remainder of the roster was ineffective at rushing the football. The Bears passing game struggled to protect the quarterback, either quarterback. Both Trubisky and Foles were sacked 18 times apiece.
Comparison to the LA Rams offense: The Rams have several advantages to the Bears situation. First, Matthew Stafford will be the starter with no competition. Secondly, the Rams rushing offense, although more diverse in 2020, was far more effective, putting up 25 percent more yards on the ground. That running game is huge in keeping pressure off the quarterback, and it helped the Rams offensive line to yield 11 fewer quarterback sacks. The Bears leaned more heavily into their passing game, but were less effective than the Rams. While Allen Robinson is a solid receiver, the Bears targets were far less effective.
Conlusion: The Rams offense has more weapons in their offense, and Stafford is here to start, not compete, at quarterback. The Rams offense in 2021 should outperform the 2020 Chicago Bears offense by a significant amount.