^^^ agree
Usually when you see a team improve or decline with a new coach, it's going to mostly have to do with the other factors Cincy is equalizing. I guess he's getting at how many wins is just X's and O's worth, and ~2 is also my guess, though it depends on the season and the games. If your team is going to play in several close games--all else being equal--then you probably get 1 or 2 of those that you might not otherwise. If you're winning or losing big most weekends, meaning your games aren't close, the X's and O's factor is going to diminish significantly.
Bud Elliot at SBN has some pretty convincing data about talent acquisition. I don't know coined the phrase "It's not the X's and O's, it's the Johnny and Joes," but it definitely seems to hold up. Alabama is Alabama not because they're coached great (they are, but so are many others), but because 80% of their roster is blue chips. Unless you have a roster somewhere in the ballpark + a QB like a Vince Young or a Deshaun Watson, you're not going to beat them. Best you can hope for is they don't have a good day.
All that said, in those close games, tactics become magnified. Maybe not pivotal, but depending on the situation, ever more crucial. I believe it was the 2012 game between LSU and Arkansas when John L. Smith was the Hogs interim coach, and they lost a close one to us. John L. Smith was not a good coach. At the end of the game, down less than a score and moving the ball on us, he decided to punt on 4th and short, even though they almost surely converted, almost surely would keep moving and score, and time would run out and probably win. But even if not, you really had no choice. I don't think either team had timeouts, or enough of them, and ARK's hand was forced. Amazingly, he called punt.....because?.....I guess that's what you're supposed to do on 4th down? LSU didn't even have to pick up a first down, I don't think, and we ran the game out.
I think they needed a FG, were almost in range, and were moving well and LSU had played like garbage and deserved to lose. He just made a horrible call that literally handed the game to us. Literally almost any other coach in the nation would've beaten us that day. That's an example of a bad coaching being worth a loss, where even a "below average" coach probably gets a win.