If you plan to hold large amounts of cryptocurrency with a long term horizon you are better off keeping them in a reputable hardware wallet. Exchanges have been known to go bust from time to time. In this scenario you would not be able to retrieve your crypto because it would be in a custodial wallet meaning you wouldn't have the keys to it. Online Wallets and exchanges are equally likely to get hacked. Users with sizeble amounts of crypto should consider taking out insurance and diversifying between multiple wallets.