Heinicke didn't play against the Bears.
And the defense played no role whatsoever in the 2021 Giants and Falcons games--which, for the record, Curl was healthy for both and Jackson actually played in both, so it should have been a detriment from your logic. And the defense played no role in the almost 11 minute drive that sealed the win at the end of the Bucs game last year. They helped the offense gain an early lead, though. But without that long-ass drive at the end that almost took up the entire 4th quarter, it's realistic that they could have just as easily lost. The best defense is a good offense, and all that.
Like I said, unless the argument is that guys like Smith and Heinicke just got lucky the defense only played well when they started, all we're doing is finding different ways of dismissing Heinicke's role in his wins as irrelevant. This is most definitely not a team that can win no matter how mediocre the QB is...they aren't constructed that way and have not had coaches that are so amazing they can make Filet Mignon out of cube steak lol...there's no linear path to the wins. And I can't quantify what he brings to the team that helps them win at least one more game than they lose with him behind center. But I'm not gonna pretend that the team is any better than it is and that Heinicke is really, really lucky and just along for the ride.
The two QBs with the absolute least physical attributes, have been the only ones to help lead the team to winning records. All the other QBs with far, FAR more physical talent couldn't do jack with the same teams. So there has to be something else those 2 QBs bring to their game that I'm guessing many don't even think about (or don't consider to be important).