It's a good question but it's also a bit complicated. I think he's the (or a) right guy for that situation. I believe that too often whether or not someone is viewed as a good coach or a bad coach ends up falling on variables that may not be as relevant to their coaching. Then again, I guess it really depends on what we mean and what, exactly, we're measuring when we say "good coach." If Kerr were coaching, say, Charlotte or Atlanta, what would people think? Probably would be fairly indifferent. What if Jim Boylen were coaching the Warriors? Probably a bad combo. Anyway, Luke Walton was present for the historic GSW run, which guaranteed him landing a HC job, but does what he did (or, rather, what he didn't get in the way of) in GS really translate into something he'd have to (more actively) do in another situation? Who knows.
Tl;dr I think it's more about the right guy for the right situation, rather than trying to create some type of objective measure of "good." Many players fall into this category, too, as they may appear great in one situation, but terrible in another, and vice versa, which is why I advocate overall fit.
