I think that we are very close to agreeing with each other. I accept some of your points, especially the one about black people perceiving racism and not trying as hard as a result (not individuals - as a whole, statistically). This is precisely why I call it implicit racism not explicit. Let's follow the route of 'not trying so hard' for a moment. If there were a Rooney Rule, then this could give them the confidence that they have a chance and hence break the vicious circle. Moreover, their perception has to come from somewhere. Can we imagine that they have just a 10% lower chance of landing a job (that doesn't seem unreasonable - there are plenty of publicised incidents of figures in the game making racist comments incl. our very own large Ron). That 10% might well result in two of a given person's mates not getting a job, so that person doesn't bother and the impact is that there are no black managers at all. Or even the fact that there are no serving black managers could create such a feeling of apathy or disenchantment.
Or let's look at this from another angle. Are we honestly saying that every single white manager is better and more skilled than every single black candidate? It beggars belief - cannot be so. Hence I conclude there is IMPLICIT racism inherent in the environment. Possibly no single director ever deliberately excludes - but the combination of all the factors brings the result that black people are misrepresented due to the colour of their skin. The Rooney Rule, a no blame, harmless & non-forcing rule, might just be the hammer needed to break the circle. Once it is broken I suspect the rule could be retired and everyone would think back and say "I cannot believe it when I think there were no black managers - how could that have been so?"
Would be interested discussing economics with you in the pub (metaphorically). I studied Maths but am very interested in Economics too - a fact that has caused me to have no natural political party to support: support a liberal (small l) caring social policy but a Conservative economic policy.