Manning had a far better record this year than Osweiler. He only lost two games, at least one of those on a bad foot.
The Broncos’ DEFENSE had a far better record during Manning’s games, many of those wins their defense got the only TDs. Notice that even though he missed a bunch of games Manning had the second highest number of picks on the year. Don’t credit the record to the QB, it’s a 53 man roster and pretty much anybody can put up points.