I mean, technically diversification is just one strategy. It's a safe way to make sure you don't lose it all, sure. But if you're sure enough about something and/or are comfortable with the risk, then less diversification becomes a viable strategy.
(Hard to argue with diversifying, but it's not necessarily for everyone in all circumstances.)
Not sure what you mean about the ICOs tho. One may go up 40x, but most of them do lousy compared to just holding btc or eth. I'd be surprised if a basket of all ICOs has outperformed ETH.
Diversification is of course a perfectly good idea in general, but most ICOs that come out are huge gambles, so the equation kind of changes to where "diversifying" into these is actually probably riskier than just holding one large coin.