Hackers can hack into a wallet, and your account on the exchange, if you do not follow the rules of security on the Internet. Therefore, it is better not to keep your money in one place. Divide them into parts. Keep something on your wallet, and some part on stock exchanges.
I don't agree with you. What is the point of holding a coin in exchange if you are going to hold it long term? I see no point to keep anything in exchange unless I am going to use it tomorrow or the day after. Everything else is in wallet, period.