So let's take a look at Illinois using the Complex Invasion College Football Production Model before and during Beckman's tenure. I will be starting with the 2008 season and move forward through 2014.
Below is a chart of the Illinois Illini offense, defense and total production rankings since 2008 along with the rank of the worst team in the Football Bowl Subdivision during the time period. More information from the model is presented below.
2008
Unfortunately, I do not have all the data to run the model before the 2008 season, so I am unable to show how Illinois performed in the previous Rose Bowl season. As such, I can only evaluate based on the data that I have and the model that I am using is the same since the 2008 season. That said, Illinois finished the 2008 season at 5-7 and bowl ineligible and played against an "average" strength of schedule (SOS) as compared to the "league" average, meaning that their actual SOS was within one standard deviation of the "league" average SOS. The Illini's best game was a victory over #9 ranked Iowa and their worst loss was to #75 ranked Minnesota. Overall, the Illini's had the #49 most productive college football team with the #45 ranked offense and the #54 ranked defense.
2009
Statistically this was Ron Zook's worst team during this time period (but better than Beckman's first season as I detail below). Illinois finished the regular season at 3-9 and played against an "average" strength of schedule (SOS) as compared to the "league" average. The Illini's best game was a victory over #79 ranked Michigan and their worst loss was to #89 ranked Indiana. Overall, the Illini's had the #95 ranked team in terms of total production with the #84 ranked offense and the #92 ranked defense.
2010
Illinois significantly turned their production around in this season although the wins and losses do not reflect the relative productivity of the team in this season. Illinois finished at 7-6 while playing against a "average" strength of schedule (SOS) as compared to the "league" average. The Illini's best game was a victory over #8 ranked Northern Illinois and their worst loss was to #89 ranked Minnesota. Illinois had the #18 ranked team in overall productivity with the #35 ranked offense and the #11 ranked defense.
2011
In Zook's last season as head football coach the Illini finished at 7-6. Illinois played against an "average" strength of schedule (SOS) as compared to the "league" average. The Illini's best game was a victory over #25 ranked Arkansas State and their worst loss was to #101 ranked Minnesota. The Illini's had the #61 ranked team (just on the other side of below average) with the #91 ranked offense and the #31 ranked defense.
2012
Tim Beckman took over for Ron Zook this season and while Illinois played against an "average" strength of schedule (SOS) as compared to the "league" average, meaning that their actual SOS was within one standard deviation of the "league" average SOS. Illinois finished the regular season at 2-10 and their worst winning percentage during this time period. The Illini's best game was a victory over #65 ranked Western Michigan and their worst loss was to #103 ranked Indiana. Overall, the Illini's had the #115 ranked team with the #118 ranked offense and the #91 ranked defense. Clearly, a year to forget.
2013
In Beckman's second season as head football coach the Illini finished the regular season at 4-8 and were bowl ineligible. Illinois played against a "tougher" strength of schedule (SOS) as compared to the "league" average, meaning that their actual SOS was between one and two standard deviations lower than the "league" average SOS. The Illini's best game was a victory over #25 ranked Cincinnati and their worst loss was to #77 ranked Indiana. Overall, the Illini had the #97 ranked team with the #63 ranked offense and the #117 ranked defense.
2014
In what turns out to be Beckman's last season as head football coach the Illini finished the regular season at 6-6 and lost to Louisana Tech in the bowl game. Illinois again played against a "tougher" strength of schedule (SOS) as compared to the "league" average. This season the Illini's best game was a victory over #45 ranked Minnesota and their worst loss was to #110 ranked Purdue. Overall, the Illini had the #93 ranked team with the #76 ranked offense and the #111 ranked defense.
Thus Illinois has performed under Beckman worse on average than Zook's worst team during this time period.