First rules of crypto: NEVER LEAVE YOUR FUNDS ON EXCHANGES OVERNIGHT. USE EXCHANGES ONLY ON THE MOMENT OF TRADING NEEDS. Or, at least, do not store more funds than you can afford to lose on random exchanges.
If you do not own the keys, you do not own the coins.
Well, but if I am a trader, what should I do next? Just everybody keeps funds on exchanges, but I prefer bigger exchanges with good security like binance, okex.
And yeah, if you have big portfolio, then I would split it between cold wallets and several exchanges!