Now that you mention it: Electrum should have a PDF-feature for that. If the user has to manually copy/paste the addresses, keys and QR-codes to be able to print one page, chances are they mess up.
It's not a bad idea. You could always propose something along those lines on GitHub if you wanted.
I wouldn't include any raw private keys, though. This simply encourages people to import them individually and run in to all the usual problems of importing single keys. All you need is a seed phrase, the first couple of addresses (configurable), and a QR code for those addresses. Perhaps with an option to include the xpub and its QR code at your chosen derivation path so you an easily create a watch-only wallet for the paper wallet and see exactly how much bitcoin you have spread across all the addresses.
The only reason websites are still in use for paper wallets, is because it's the most easiest way to create them.
But the paper wallets created by such websites are outdated and should really no longer be used at all.