I agree with the author,in recent time, often appear to news about the hacking of exchanges.But I keep money in my stock account on exchange. After all, there are times when you need to urgently buy or sell something,and while you transfer from wallet to exchange-you lose time.
Just choose a secured exchange, it's much practical to hold some in exchanges especially if we really plan to trade, we will spend a lot in transaction fees if we plan to keep it on our wallet.
That is what we must do if we want to keep the coins in the exchange, so we don't have to afraid if we are getting hacked.
There is many secured exchange we can use and with activate 2fa, email verification and else, we can make sure the account will be secure.
Besides that, the exchange will protect us from hackers, so we don't have to worry.
I still keep some of my coins in many exchanges like poloniex, binance, bittrex, kucoin and else and I always activate 2fa to protect me.