" Without a healthy and diverse community of participants, the quality of our content will suffer."

"Quality of our content will suffer" doesn't imply that young, white men from the developing world can't write quality content. It implies that a multiplicity of views is required to reach a certain standard of quality, and that we aren't achieving that now and won't unless we have more diversity. Perhaps this can be reworded to clarify.

Regarding data, I think it would be good to track this to the best of our ability. The best data we have on diversity is the UNU-MERIT study, which has well-known problems. There's been no work done to my knowledge linking diversity to the current lack of quality on any of the Wikimedia projects. However, let's not get too caught up with data. Wikimedia is built on the premise that a multiplicity of views represented in an open, shared space will lead to high-quality content. If we're suffering in this regard (as we our), it makes sense to prioritize this.

Finally, regarding reality vs platitudes. We can make Wikimedia more diverse. There are many things that could be done, and by calling it out as a priority, we will hopefully galvanize people to take on some of these ideas.