Subject: Re: 90/10 or 10/90?
A) market is drastically, just damn stupidly, overvalued

This one is very popular and currently quite defensible for the US cap-weighted market.

B) you must hold a lot of cash and some Berkshire

Don't ever remember hearing that one. I hear it the other way around: hold a lot of Berkshire and some cash.

That's what I do. Plus some index funds.

It's interesting (to me) that over my 24-year investing career it probably made little difference whether I put money into Berkshire, like I did, or into an S&P500 index fund, like Buffett has recommended.

24 years BRK.b vs SPY:
https://www.portfoliovisualize...

Not much in it. Slight advantage Berkshire.

Going forward, well I think Berkshire has a better return expectation, but I've thought that for 20 years...