I agree with you, if we holding coin on the exchange will be many risks like coin hack, exchange stopped and other problems.
I recommendation use hardware wallet like ledger or trezor because of high security.
But you must keep the 24-word seed to recovery.
Even with the exchanges our funds were secure. For this we need to select the best exchange service, because one with the best reputation will never let their users get scammed or get into any security issues. Holding on exchanges and different trading platforms were good for daily traders.
This is not a problem if you are holding coin on any exchange for a long time because the exchange is yours and you will need to handle that so where the risk or difficulty will occur? The best choice is to trade without any friction and to sell rapidly if you are in profit.
You will must be holding coin for a long time if you bought the coin on high price and then waiting for the price to go higher. So this is a false decision to buy coin in a high market, you need to buy in a low market so as to remove and prevent yourself on holding coin in an exchange for long time.