For openers, I think all posters in this thread have made good points.
But this is a multifaceted issue and here goes...
1. Yeah, there was a lot of talent on this roster when McVay walked in the door. Largely misused, but it WAS there. Goff and Gurley immediately morphed from bust to Pro Bowl status.
2. McVay quickly made excellent asst coaching hires. The importance of that can’t be overstated.
3. Snead was wisely retained. His impact has been immense. This turnaround could never have happened without Snead’s inspired personnel moves. I credit Demoff for retaining Snead, btw.
4. McVay/Snead rapidly offloaded players that were inadequate and/or not scheme fits. They were very decisive and sent a powerful message in the process.
5. S&M have made two consecutive brilliant drafts, considering the picks they had to work with.
6. They also have made some exceptional FA and trade moves to stock up their roster.
7. McVay brought in a whole new culture. Some outsiders may have scoffed, but the players sure bought in.
8. McVay also brought in an exciting and extremely effective MODERN O. One so advanced that other teams are still having trouble coping with it and are also trying to copy much of it.
I submit to you that each of the above were necessary in order to effect this record setting turnaround. IOW, there were many necessary pieces to this puzzle.
Good luck to other teams assembling the necessary ingredients for another such turnaround. I suspect that they will be fortunate to achieve even three of them. Lol.