It's not that you shouldn't be using exchanges per se, it's just that you shouldn't leave your entire holdings on exchanges(which surprisingly a lot of people still do). If you trade with like 5% of your total holdings, then only leave that 5% on exchanges. And just withdraw the funds when you plan on stopping trading for a while and such.
No one knows when exchange will be hacked, even if you risk and leave funds on exchange for some hours, there is a chance that it will be hacked and your funds will be stolen. And if you deposit/withdraw money on each trade, I hugely doubt you'll get any profit because nowadays there are a huge fees on transaction and everytime I opened my Electrum wallet, it was always warning me that fee was very high. Paying 5% of your initial capital in bitcoin transaction fees can't bring you a profit in trading. That's why I asked what to do and if you trade with 5% of your total holdings, even if you have high capital, it will be just a waste of time and playing for nothing.