The most recent example of a solid turn around where it included a new coaching staff and scheme change without too much personnel change was probably the LA Rams when McVay took over from Fisher (2016 to 2017). They went from 4-12 to 11-5 the following year, making the playoffs. Funny enough, Quinn was on that team. 2017 was Cooper Kupp's rookie year. They didn't have a 1000 yard receiver and Gurley was the 2nd leading receiver on the team.
So, if you want parallels, IMO, that is probably the best one of what could happen if everything clicks. But keep in mind, that Rams team had Aaron Donald and Quinn on defense and they had Whitworth at LT. So, while the Bears literally have the same Robert Quinn, they sure as hell don't have an Aaron Donald or Andrew Whitworth to solidify both the lines. And while I like Montgomery, I would never mistake him for an uninjured, prime Todd Gurley.
The Bears had 6 wins last year and they are still playing in the weaker NFC conference. I think it's odd that people think they will do worse this season than the disfunction that was last season. I don't expect the Bears to make the playoffs, but I do expect them to compete and not really be anywhere near last place.