All Exchanges are not created equal and one can still lose exchange coins due to exchange getting hacked or shutdown due to government regulation or some other reason. So it is useful to keep a good portion of your coins in your own wallet. To reduce the risk, use multiple exchanges and multiple wallets too.
Complete agreement. The only thing that can complement this answer, you can use the hardware wallet to provide more security to your coins, but it is worth noting that it can not store all the coins.