I enjoyed the article.

However, I can't let this quote pass unchallenged...
"The invention of the first open-ended mutual fund in 1924 by Massachusetts Investors kickstarted the diversification era"

The CFA claims to be a global association, so it's puzzling that you think collective investments offering diversification began or first became popular in the US.

The investment company concept dates back to Europe in the late 1700s, when "a Dutch merchant and broker... invited subscriptions from investors... to provide an opportunity to diversify for small investors with limited means". (Quote from The Origins of Mutual Funds by K. Geert Rouwenhorst).

Actual successful investment companies, as we know them today, date to the 1860's. The Foreign & Colonial Investment Trust, founded in 1868 and has just celebrated it's 150th birthday, "was the first collective investment scheme in the world". It's original prospectus highlighted the benefits of diversification, promising "to give the investor of moderate means the same advantages as the large capitalists in diminishing the risk of spreading the investment over a number of stocks". (Quotes from Wikipedia pages for "Foreign & Colonial Investment Trust" and "Investment Trusts").

By the end of the 1880s investment companies were booming in Britain, with over 80 companies in existence. Diversification was one of the main selling points and was fully understood as a major benefit by the investing public.

It would not surprise me to find even earlier examples. Diversification is not a modern concept.