You don't. Hacks target the exchanges wallet by finding exploits and not the user accounts separately. If you want your funds to be safe, use exchanges for trading only and withdraw to your personal wallet.
Listen to him. What he is are saying is true. The problem lies on the system itself of the exchanges. But there is no way that they can hack your hardware wallet unless they force you to spit out your seed, or when you get phished online. Almost all exchanges nowadays are only came from scratch and some don't even know that their exchange will reach that far, that's why they are having a real deal maintaining the security of their exchanges. Imagine if some reputable company (facebook for example) decided to have a cryptocurrency exchange and the people that are working there has an A++ degrees in different fields of computer in the most prestigious universities. Do you think that they can still put a dent in their security? Give it time and these exchanges will improve too. In the meantime don't fully trust them and always leave your funds in your own personal wallet.
Even if they had rock solid security we must never trust in exchanges completely that is the whole point of bitcoin, we need to have control over our own coins and use exchanges only when you need it, traders do not have too much of a choice but for the rest of us leaving our coins in an exchange is a terrible option since you are trusting that a third party service keeps your coins safe and does not exit scam you.