Hackers are everywhere. If you are not using hard wallets, you are equally exposed to hackers. Even if you are not storing them in the exchanges, you are still exposed to the possibility of hacking. Remember that even MEW, Mist, etc. have hacking histories. If you are only HODLing your coins, you better choose hard wallets. But if you are constantly trading, you have no choice but to keep them in the exchanges. Just install 2FA and keep your passwords and keys away from anyone.