A short premise: HW wallets and password managers have surely different scopes, but they both seems to cover what I'm interested in, which is securely storing a private key.
Hardware wallets: a device such as TREZOR (or LedgerNanoS) is usually recommended for storing a PK because it never expose it to the machine operating the Ethereum client, so your PK can't leave the device. Seems good so far, but what if the device breaks? You can then recover seed from a paper backup. This seems to me the most fragile passage: a paper can get lost easily, can be stolen, etc. Otherwise a password manager db can be easily spread into several clouds, storages.
Password Manager: a SW such as KeePass can encrypt very securerly (Argon 2 for key derivation and AES256 as cipher) your PK. Assuming you don't directly store the PK but a Keystore File (with encrypted PK), you'll just need to enter its passphrase in MEW. The only vulnerability that comes to my mind is about keyloggers, then it can be hardened using a keyfile + passphrase authentication in KeePass. A KeePass db is strongly encrypted and can be easily backed up.
Which is the actual advantage in using a device like TREZOR here?