No air-gapped machine and a random flash memory stick (for storing the backup of the private key) can be considered as secure as the secure element.
I love my Yubikey, but I generated the keys on it on an air-gapped machine and wrote them to two DVDs and the Yubikey.
Unless you can get everyone to send you messages to encrypt them to both your main key and your secondary backup key you will regret not having backed up your primary key.
You can't have both, I think. With a physical key your only concern is the physical security of the key. One should print out the revocation certificate, though.
I don't think many people lose their home keys or get them run over by a car. It's just a matter of making that a priority.
All it needs is some idiot emptying his drink over your pants to fry an USB device. Or a drunk driver crashing into your bike and breaking the device.
Print out your passphrase-protected keyset, put it together with an encrypted copy of your most common passwords (I know no one uses a dedicated password for every site!) and your KeePass/Keychain/... database in a bank safe and one in your home's safe.
Put the password to said DBs in your will (or deposit it at a notary's office), so that in case you die your relatives will be able to shut down your online presence, but not if either the bank, your safe or the notary get busted.
Anyway, I think it's very risky to rely on single physical item for your private key storage.