Again we saw an exchange got hacked. There would be nothing to hack there if people didn't keep their coins on exchanges! For the love of Dog (lol), don't keep your coins on exchanges, start practicing safety, this is your investment we are talking about!
so far I have no problem storing altcoins on several exchanges, I think by making security that is tight enough to make it more protected. I have bitcoin and altcoin on hitbtc and binance. there is no problem until now I have kept it for almost a year.