Indeed. Everyone being brilliant would of course foster diversity, as well as overall cultural capital. I might be wrong, but it seems obvious to me.
To me the original quote seems to spring from an elitist mindset and akin to saying there's no diversity in painting anymore because everyone uses rectangular canvases. It's not the brilliance that makes you diverse, but rather what springs from it.
No matter how brilliant someone is, they still only have limited time. Increased capabilities increases the options someone has within their available time. There is incredible diversity in the goals and the specific capabilities people bring to whatever they are doing, increasing the capabilities could only increase the diversity.
To me the original quote seems to spring from an elitist mindset and akin to saying there's no diversity in painting anymore because everyone uses rectangular canvases. It's not the brilliance that makes you diverse, but rather what springs from it.