There's always an element of chance in hiring a new head coach. But, typically there are indicators, predictors of success, that form the foundation of the decision to hire. So far, the only indicators of success I've seen are association with Belichick and personal knowledge of Grier. Since I don't know what Grier knows, I can't evaluate that one. But I can say that it does not appear the New England coaching staff has ever had a culture of teaching coaching.
It's one thing to carry out an order, be a good soldier. I think the Patriots organization does a fantastic job of that up and down the tree both coaches and players. That is the basis of that entire organization, and why their motto is "Do your job." Because a marine's job is not to question why, a marine's job is to do or die. Belichick has a lot of military exposure, and he runs his teams in a military manner. Information is on a need to know basis. Belichick listens to all of the strategy, then chooses the course of the ship, and then implements the strategies he wants, both on offense and defense. Of his coaches that have gone elsewhere, the only ones I can recall him really missing/fearing were Josh McDaniels and Romeo Crenel, both of whom seem to have been very good coaches in their own right.
Most coaching staffs have a group pow wow where the coaches share information freely across the entire coaching staff, or across the entire offense, or entire defense. I'm not sure Belichick does a lot of that. So his staff never knows the full story, only Belichick does. Sure, nothing ever leaks. Sure, it clearly works when you have someone as talented as Belichick leading the way, and it compartmentalizes information making it harder to be caught cheating … and Belichick doesn't seem to have any compunction about cheating either.
But there is another element missing from the Belichick coaching tree. On most staffs the more experienced guys TEACH the younger coaches why they do things, what consequences they're avoiding by making those decisions, how it all fits into the larger picture, why tactic X works for some players and not for others, examples of their previous coaching experiences and how these things worked and why they worked out that way. Just as teaching is a crucial element in coaching players, it is a valuable element for young coaches to be taught by more experienced coaches.
Belichick not only doesn't promote coaches teaching coaches, he discourages it. So his coaches end up being good marines, people who do exactly what they're told and implement his decisions. For most things, they can figure out the why, but maybe not much over half of them. There are a lot of decisions where they misinterpret the why or they simply don't know the why, and so they end up making lots of bad decisions and having difficulty putting those into context to effectively learn from those poor decisions.
I'm not knocking Bill Belichick's coaching methodology, it obviously works for him. But I have zero faith in that methodology for his coaching tree. I give Flores no credit for having worked with Belichick this long, because I don't see evidence of his success without Belichick, and I have no faith that Belichick helped any of his staff learn. So essentially, without some other independent indicator of success, I can't get behind the Flores choice if that is the one we make. Nothing against Flores, but Bill Belichick doesn't help coaches learn.
