" Berkshire is a big position in cap weighted indexes which have been rising strongly, so it's tracking the market exactly as you'd expect. No mystery at all. There is no evidence whatsoever of a particular fondness for Berkshire shares this year, relative to anything else."
...
What? How much is brkb up YTD? How much are the top 10 in the spy up YTD? What about the other 490 stocks? Thanks.

The S&P 500 is up 17.6% year to date including reinvested dividends.

As has been widely commented, a lot of that is due to the very strong performance of a few very large firms. The average S&P 500 firm is up 10.8% (the equal weight index total return).
Berkshire is up 13.4%, between the two. Nothing particularly evident in the way of company-specific exuberance, nor pessimism.

Of course, all of those figures above are measured in US dollars, which have shrunk a lot this year. (the US dollar index has fallen from 108.5 to 99.51 year to date).
Measured on a trade weighted basis, a much better approximation of the true general purpose purchasing power value of a shareholding--
S&P 500 up 7.9% including dividends
S&P equal weight up 1.6% including dividends
Berkshire up 4.0%
FWIW, in euros the average S&P 500 firm is down -0.7% year to date including dividends.

Despite all the Sturm und Drang along the way, it hasn't been a very noteworthy end result, all things considered.

Jim