Final thoughts on Philip Rivers' career
Simply picking the best coach that Rivers played for isn't the easiest task in the world, given all of the other factors that go into it. Each coach, no matter how good or bad they were, all had chances to go far but couldn't for whatever reason, both in their control and out of their control.
What if the Chargers and Colts win their division in 2018 and 2020 instead of losing a tiebreaker? What if the Chargers have a halfway decent special teams unit in 2010? What if Rivers had an effective running game and offensive line during his prime?
Rivers took over 30 sacks in every season from 2010-2019, while never reaching 30 sacks in a season from 2006-2009.
Speaking of the 06-09 teams, what if Marlon McCree doesn't fumble in the 2006 playoffs? What if Rivers, Tomlinson, and Gates are all healthy for the 2007 AFC Championship Game? What if kicker Nate Kaeding actually made his kicks in the playoffs in 2009? What if Marty Schottenheimer isn't fired after a 14-2 season? With the Chargers, you could go on and on with the what-ifs.
The best way to look at it is that we got to watch one of the greatest QBs in NFL history put on a show for 17 years, 16 of those seasons with the Chargers. On an ideal Philip Rivers coaching staff, the best answer would probably be Schottenheimer, although we only got to see those two work together for one season.
We also don't know how Rivers and Schottenheimer would've worked with Rivers taking more control of the offense as he matured, as Schottenheimer's philosophy worked more around leading with a strong running game. Frank Reich would 100% need to be included, given that Rivers looked the most comfortable when Reich was on his staff, despite what the running game looked like.
Rivers also had 4 of his 5 highest completion percentage seasons with Reich on his coaching staff. You could also say Turner because he lasted longer than any other coach that Rivers had, but a lot of Turner's success could be credited to inheriting such a great team, and after a lot of that team was either injured or left, Turner struggled to make the playoffs.
Leadership would be another important factor, something that Lynn was great at after the lack of leadership with McCoy. But those two, like really all of Rivers coaches, always had one similar flaw, not being able to finish when it mattered most.