Interesting that his performance was essentially identical to the S&P over the past 30 years (Sortino 0.72 vs 0.69): https://testfol.io/?s=jJ4P0GrZxLi

I wonder how much is due to the market becoming more efficient, vs Berkshire's size / market impact?

How do you figure? The portfolio looks to have performed roughly the same as the S&P.

That is wild.