the traditional "monkey with a dartboard" rate of total return from stocks in the US has been inflation + 6.5%/year, the average return from the average stock in the average year.

Right. That´s the "Bogleheads" approach to investing if I am not mistaken, holding index funds longterm. Also what Warren himself advises know-nothing Investors to do.

But: Sure, valuations are stretched all over the place so this is a tough starting point.

That´s one point. That as you said numerous times Berkshire is valued reasonable while the S&P is not.

But that´s not a one-off event. It will repeat someday. There will be another .com bubble, another GFC, another whatever. And the "Bogleheads" during those times, in both directions, during bubbles and during crashes, are then much more challenged to adhere to their investment philosophy than the LT Berkshire Investor. And index investing only works reliably when you do it purely mechanically, not when you chicken out during the next crash, or ccash in profits and are unable to get in again. Plus even if you stomach a 50+% drawdown you may need an unforeseeable time horizon to recover, a long time to get weak and sell (at the worst point). Huge mental challenges.

On the other hand while Berkshire had long stretches of it´s price going nowhere it did bot crash as extremely as the S&P/Nasdaq can do, and it´s price at least remotely always reflects it´s value, does not diverge wildly from it (which is the very reason why there is a reliable relatively narrow Price/BV channel). Overvalued, undervalued, yes, but nothing really extreme. It´s beautifully boring.

Btw, re the thread title "A New Berkshire": I don´t see that. I see a new boss at the top of the same company, a company carefully constructed by Warren & Charlie over decades.