However, with each passing year (every day, actually), the size increases, and it will take longer to synchronize a full node.
On the other hand: with every hardware upgrade, it's a lot faster again 
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I just want a way to make these backups, and when restoring, for example, from one laptop to another, move the (updated) backup to the laptop with the outdated Bitcoin folder, without having to delete the blockchain/blocks/database, allowing the updated backup to complement the outdated laptop's database.
For Linux, that's what rsync is for. But note that different Bitcoin Core downloads don't have the exact same blocks files, so if you're trying to "complement" one node with data from another note, it could still require copying almost everything.