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 cash 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.

Is above really true? Is it actually easier to be in BRK than SPY in a big crash? More importantly, will be it true in the future? Next time everything goes to hell, will you really have more faith in Greg than the collective wisdom in SPY?

The real point is it doesn't have to be an all or nothing approach. There is no law against holding both. BRK vs SPY has been a constant theme on this board since SPY 1500 and here we are at SPY 7800. An ungodly amount of money has not been made because of the persistent bias against SPY.

Why not flip from BRK vs SPY to BRK & SPY. They can coexist just fine!

Whatever portion of your net worth you want in equities, simply split in equal measure between individual equities (BRK, etc.) and broad index funds (SPY, RSP, QQQE, etc.). Come hell or highwater, one is much more likely to maintain investing discipline this way compared to BRK all-in.