It was a common argument during the Sacco era, and immediately after he was fired. It was more or less articulated here by Terry Frei:
Though Frei twists the argument against Sacco to make it appear as if the argument is that Sacco was the only problem. I don't think even his most vehement critics would have argued that. And certainly, the other changes the Avs made in the off season, starting with the restructuring of the front office, addressed many of the issues Frei argued needed to be addressed (that few of Sacco's critics would disagree needed to be addressed).
The argument was never that Sacco was THE problem, simply A problem. There were plenty of skeptics that felt even if he was not the best fit as a coach, the problem he represented was minimal compared to the makeup of the team and the defense in particular. The crux of that argument essentially was that no coach could get more out of the collection of players Sacco had to work with. Those making the argument were certainly not optimistic about the prospects of Sarich, Benoit and Guenin replacing O'Byrne, Hunwick and O'Brien on the roster.
What has Roy's start proven about the impact of coaching? Yes the sample size is small. Yes, Sacco was 10-1-2 in his first 13 games which is not appreciably worse than 12-1. This hot start simply feels different than that hot start, and look no further than the defensive play as proof. The team is playing cohesive team defense, something we had not seen at any point really in Sacco's tenure. The difference is undeniably dramatic.
It was considered a unsophisticated and too emotional argument to blame the coach. Frei calls it "cliched and oversimplified". It's the players who win games, not coaches. So it goes. The argument was popular. Many of you reading this were making it. But unless Roy and the Avs are experiencing another flash in the pan start, it would seem the arguments against the impact of coaching has been obliterated. Yes the front office has changed and there's a different attitude, but the most significant change to the roster was the addition of a barely 18 year old rookie. Clearly, the most significant change the Avs made in the off season was the coach. At this point there might not be many people left who would argue that a coaching change wouldn't make much of a difference, but the argument was made, and I'm interested in reading elaborations of that argument from those folks given the current perspective.