Peter Brandt as actually gotten this wrong, it is true that some altcoins are shitty and will not even exist anymore before the five years time he's saying, but more it can not be upto 99% of the altcoins. Coins like Ethereum, Dash and Doge will keep existing for a very long time.
The problem in here is, there are a hundred of projects created daily. If we are counting it, approximately around 36.500 projects created yearly. That means he's mathematically not wrong about it because 100 projects can be considered as 1% of our total altcoins right now.