Are you kidding with diversification is for idiots? Every financial guru who isn't an idiot will tell you otherwise. You hedge against stocks with bonds. You hedge against inflation with gold and silver. It's the most common sense you can possibly do with your money.
By the way, didn't Cuban get rich off the dot com bubble?
From Wikipedia:
"That year, during the
dot com boom, Broadcast.com was acquired by
Yahoo! for $5.7 billion in Yahoo! stock.
[35]
After the sale of Broadcast.com, Cuban
diversified his wealth to avoid exposure to a market crash."
https://en.wikipedia.org/wiki/Mark_Cuban