Why would you want to generate something elsewhere (which could be compromised) and then import it?
I dont intend to generate keys elsewhere. They were generated before "seed" wallets existed.
Do not let hardware wallet or having the coins on any other wallets to fool you if you are not planing to spend the coins. As you do not plan to do anything with any of the coins but you want it to be old on blackchain as it is now, then do not import the paper wallet at all and let it be as it is now.
If you have it on a hardware wallet and still have the paper, metal or any other backup, it is still the same like you have the paper/matal backup but you just have to make sure that eproperly backup the seed phrase. Having like 2 or 3 backups. You can even prefer encrypting the backups instead on a storage device like a memory card through an airgapped device.
Best alternative
Alternatively, you can get a cheap laptop. Make it airgapped and run Electrum on it. You can import the seed phrase on Electrum. It is cold storage wallet and secure.