It only makes sense to me that a Paper wallet is meant to be created offline to increase the security and therefore it makes further sense that the Sweep/Import option should also be done offline first and then encrypted before you go online again.
The automated Encryption and Decryption of the Private key to import/sweep the wallet, would reduce the risk of the private key being compromised during the process to sweep/import these wallets, when you go online.
Offline
Step 1 - Scan QR code on Paper wallet and retrieve the Private key
Step 2 - Insert Private key into App
Step 3 - App Encrypt Private key
Step 4 - Insert Bitcoin Address where coins will be swept to
Online
Step 5 - Go online
Step 6 - App still running, Click on "Sweep Paper Wallet"
Step 7 - Application automatically decrypt the Private key and sweep the coins from the paper wallet onto the Address specified in Step 4
Done
It seems to me that you are conflating "offline" with "air-gapped". An air-gapped system is a system that is
never online and/or lacks the ability to even connect. The idea of using an air-gapped system is that that system contains your private keys
and no other system does, ever. So, there is simply no way for a hacker, no matter how clever, to siphon away your private keys(1).
It doesn't matter very much if you disconnect a non-airgapped computer while you perform sensitive operations because a hacker may have installed some malicious code that is recording your session whether you are online or not. The moment you re-connect, the malicious code begins "relaying" its session recordings back to home base.
For reference, here's the wiki on
cold storage.
(1) - There are still risks. A Windows system with autoplay can launch code from a dirty USB key, for example.