it’s a valid question and I’m asking him to look into this and give it serious consideration. He says he will, but it’s “complicated”.
Of course it's complicated. If there was one single, easy solution, it wouldn't be a problem any more, companies would have just done it.
He is right that there aren't as many women capable of applying for executive positions - but a large part of that is because the entire pipeline is the problem. Yes, it makes sense to put someone with a proven track record forward, but from the very start, men are more likely to empoyed and promoted for their potential and women for their achievements. Men are more likely to be given high-profile projects, which gives increases their profiles and builds that track record, so they're increasingly likely to be given the high-profile projects and so on, and others just don't get those opportunities.
What processes has this company in place to make sure men and women are judged equally for recruitment and promotion so that unconscious bias doesn't discount very capable candidates? What processes have they in place to make sure that there is a pipeline of female talent working at all levels on the ladder, being given opportunities to develop their capabilities, do there will be women with the requisite skills and experience to go for the exec roles? Do they have a women's network, to make sure women are supported?
It's not an easy problem, but he's lucky - there are about a zillion articles and consultants and courses and other resources which have looked at the barriers to women reaching exec positions, and how to reduce those barriers and increase the numbers. They'll probably be able to get rid of some of the mediocre, inadequate male managers in the long term, too, because God knows, there are enough shit men around in businesses - but women have to be so much better than men to be judged as equivalent.
Even if he's moving on, these questions are relevant to those who take on the role after him, and to all his other businesses.
A quick Google will probably give him a lot of information about companies with no or only a few women on their boards. There's no shortage of info on this sort of thing out there.