I didn't get the impression that Buffett was talking short-term, or about alt-coins. He seemed to be saying that cryptocurrency in general and Bitcoin in particular are going to go down in history as fads without a real, sustainable value proposition. At the same time, he claimed personal ignorance as to what crypto is and how it works, which is why I feel free to dismiss his findings even though he's Warren Buffett.
Yes, BTC is overdue for a huge correction as way too much of its current market value is based on hype.
Yes, a lot of the other coins are not and never have been anything BUT hype (including Dogecoin, which never pretended to be anything but a joke), and at some point a lot of them are going to implode into punch lines and then into infinitesimal footnotes in search engines.
My personal bet (and where I'm putting most of the very little money I have in crypto) is that Ethereum will be one of the long-term survivors/thrivers.
I take single-digit-USD flyers on the occasional small coin that this or that analyst convinces me has potential.
The instant it became obvious that the big players in Old/Wrecked Bitcoin (BTC) were going to renege on the Segwit2x deal and keep fees high and transaction times long, I got rid of what BTC I had left, and don't regret it (I had very little left and would only have made a few hundred dollars if I had waited for it to hit e.g. $15k). I've got a little (very little) Bitcoin Cash and plan to hold it and maybe get some more.