Three wins is a HUGE difference, especially since you don't seem to be considering the fact that 1 or 2 of those wins could come over the Packers. The Bears went 1-5 in the redzone and a turnover on downs from the 25 last game. They left enough points on the board to win that with Mitch Trubisky. Watson most likely at least keeps them in it Sunday, wins Indianapolis, Detroit, Minnesota, maybe even New Orleans, Tennesee and LA Rams and they'd be playing the WFT this week in the playoffs at 11-5.
Also, the defense really isn't THAT bad. They are 12th in the league. That's still above average.
Lastly, Watson's contract is not crazy at all. His cap hit for 2021 is a meager 15.9Mil. People want to pay Trubisky that much money. It goes to 40.4Mil in 2022, but the Bears have 98M in estimated space that year can clear a TON of space that year anyway (Hicks, Graham, and Fuller, if not cut this year; Quinn, Massie, Leno, even Mack). After 2022, Watson only has 10.8M dead cap. You could cut him and save 30M, but why would you want to? 42M in 2023 is a lot (not for a top 5 QB), but then the last 2 years he goes down to 34 and 32Mil cap hit. And there's always the extension option after 2022. Give him more guaranteed money and possibly get him at a discount.