on the hardwallet the wallet owner must scan the wallet for each transaction, otherwise the transaction will not be fulfilled
No, this is not safe, scanning QR codes for every transaction might sometimes lead you to a scam, there are too many reports about this, scammers tricking the QR codes since codes are almost similar and design and no one will notice if you will send your Bitcoin to the scammer address.
nankers isn't very good with English and maybe he wasn't talking about scanning QR codes. Maybe he wanted to say that you need to check and physically confirm the transaction details on your hardware wallet. The screen will show you the destination address, the fees, and the amount being sent.
Manual input is still good because you can manually check like checking the Bitcoin address last 3 digits and the first 3 digits.
That's no longer good enough. There was a post here a few months ago about someone experimenting with clipboard hijackers for hardware wallets. I can't find it now though. Your generated address would be replaced with one that is made up of the same characters with only a few changes. Checking more than just a sequence of 3-4 characters is recommended.