it is indeed safe but be careful not to corrupt it. Online wallet is also safe but only use the official wallet of the coins, never use 3rd party who offers universal wallet.
It's best to use hardware wallets, also there are some universal wallets with good reputation and performance, whereby users have total control of their private keys like Trust wallet and Atomic wallet. If I'm holding so many coins, normally I'll sort for a universal wallet to atleast WATCH my holdings even if I don't want to import (that's if I decide using the official coin wallets). Even with hardware wallet, you can still lose your holdings if you don't back up properly.