If having more scoring opportunities or more high-quality scoring opportunities doesn't say anything about whether you deserved to win a game, then I don't know what does. As I said, it's not perfect, but over the course of a season it provides a decent picture of how deserved a team's position is.
Brentford, for example, fired Warburton after he got them 5th in the Championship and in a playoff promotion spot, because the underlying data didn't stack up. So, if teams use it, I guess it can't be that off.