I think it's more nuanced than "Buffett was not a great stock-picker".
cnbc.com - Buffett really was not a great stock picker swedroe on investing

“Warren Buffett was generally considered the greatest stock picker of all time. And, what we have learned in the academic research is Warren Buffett really was not a great stock picker at all,” Swedroe told CNBC’s “ETF Edge” this week. “What Warren Buffett’s ‘secret sauce’ was, he figured out 50, 60 years before all the academics what these factors were that allowed you to earn excess returns.”

A better way of phrasing it might be: Buffett has been a great investor because he identified these factors before anyone else (and used a bit of leverage).
Not so click-baity, though.

It'll be interesting to see if using these "factors" does lead to excess returns. So far it has not. We are early days into a 50-60 year test.

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I didn't know of this Swedroe book:
Think, Act, and Invest Like Warren Buffett: The Winning Strategy to Help You Achieve Your Financial and Life Goals Hardcover – December 11, 2012

In Think, Act, and Invest Like Warren Buffett, Swedroe provides the foundational knowledge you need to:

Develop a financial plan to help you make rational decisions on a consistent basis
Determine the level of risk that's right for you, and allocate your assets accordingly
Build a low-cost, tax-efficient, globally diversified portfolio
Manage your portfolio by rebalancing periodically to maintain proper risk levels
The beauty of the Buffett approach is its profound simplicity: follow the basics, keep your cool, and have a sense of humor and humility.

Hmmm. That's disappointing.

He's also using the Buffett name to hawk his latest book:
Enrich Your Future: The Keys to Successful Investing 2024

He is quite prolific, which is surprising, given the title of his 1998 book:
The Only Guide To A Winning Investment Strategy You'll Ever Need: Index Funds and Beyond--The Way Smart Money Creates Wealth Today Hardcover – May 1, 1998

lol