Please have a look at your own chart. It was exactly the other way around. Berkshire went down BEFORE the dotcom collapse, during the years every High-tech stock went up. I know this so well (and your chart shows it too) because at the very lowest day I bought my first Berkshire shares (thanks to a Jim Cramer yelling that very day: "Regarding Berkshire there is only one thing to do: Sell! Sell! Sell!". Thank you, Jim!).

Berkshire went heavily down not in the era of the bursting of the dotcom bubble.
It went down in the era before, the dotcom hype era.
And went up in the era of the bursting of the dotcom bubble.

Like I said, Berkshire got cut in half in the dot com era, hitting a low in March 2000.
The dot com mania continued another 6 months, until September 2000, then began its multi-year decline.
Berkshire didn't regain its previous high until November 2003. many years before SPY did, of course.

This was fine for me at the time. I'd just started investing. I bought all the way down.
It had to be painful for those living off their Berkshire shares at the time.
Wouldn't be so good for me now. I'm planning on living on my Berkshire pretty soon, with a large cash buffer just in case.

Point is, Berkshire has been cut in half twice in my ownership era.
I think it best to assume there will be similar declines in the future.
Might be when SPY also crashes, might be before or after.