From an always above average, sometimes great defense and a below average to average offense under Lovie and co., to an above average, sometimes great offense and below average to terrible defense under Trestman and co. Kansas City now a powerhouse with Reid etc. Really shows just how insanely much more important coaching is than any other aspect of the game.
Its not like the defensive personnel changed a ton, obviously the injuries hurt alot but they were really bad even in the first few weeks pre-injuries. The offense is definitely clearly better, but would have gotten a little better with the new additions under the former staff as well, though most likely not as good. If i had to guess i'd say the Bears would be a better team under last years staff, granted there are a lot of variables, injuries etc. but its hard to believe the defense would have been even close to this terrible. Trestman and co. definitely have their work cut out for them the rest of the season.
Fun fact: The bears have the best turnover margin in the league, and behind only Seattle in takeaways with 18(seattle has 19), yet still have given up the most points in the league besides Jacksonville and the Giants who both have been historically bad so far this year. I can only imagine how bad the Bears will be defensively if/when the takeaways slow down a bit. Add in the injuries and its looking like a very good chance the Bears could end the worst defense in the NFL this season. Quite a drastic change from perennially being a top tier defensive team for the past decade plus.