Exchangers are not safe as they can be hacked and if this happens you can lose all your coins.
But lokal machine can also be hacked, so we gat a little problem here - everything can be hacked

Hacking any machine is only matter of time and resources. But exchanges can not only me hacked - they can turn scam, and tell people they were hacked. In that case using wallet on own machine is much more better. So if you operate with crypto - exchanges, if you a long term holder - only own wallets, especially consisting hardware will be great for next year or two - perfect variant