IMO coaching and scheme had little to do with Russell's failings last season. Having watched a good chunk of his games, there were lots of times where he made some very poor decisions, didn't see open receivers, threw into tight windows when he had easy first downs had he ran, things like that. A prime example is the overtime loss to the Colts where he had KJ Hamler wide open for an easy TD that he passed over in lieu of a covered receiver at the back of the end zone. For a quarterback that has been starting for 11 years, that's not a coaching or scheme problem.
He did the same things in his first season with the Broncos that he was doing in his last few years with us, the most obvious of which is holding onto the ball too gawd damn long.
Last season, Russell's time to throw was 34th in the league. There were only 2 other starting QB's with 300+ attempts (Lamar Jackson and Justin Fields) that took longer than him, and they were at least 8 years younger and much more of a running threat. Russell's holding onto the ball so long was directly responsible for his taking a league leading 55 sacks, a stat made worse by his playing in just 15 games. IMO he still hasn't come to grips with the fact that at 34 years of age, he's no longer a spring chicken.
That's going to be Payton's biggest challenge, first to get Russell to recognize the problem and secondly to put him in a position to correct it. I'm not saying that Russell is unfixable, but he's going to have to make some significant changes in his game if he's going to make it happen.