You only need to store the most recent blocks for security to verify new blocks. 5GB– the minimum Bitcoin Knots, a variant of Bitcoin Core, allows 3 days of blocks. A chain rewrite/51% attack is unlikely to last 3 days because of the probabilistic grantees.
So the state for all addresses ever used fits in those couple gigabytes? Plus of course full state for a few days for longest-chain purposes, like you wrote.
I thought the majority of the hundreds of gigabytes consisted of dormant and throwaway addresses that still have some value on them, but it sounds like I've got the wrong impression and by removing transaction history for empty addresses and other historic block data, it's only a few gigabytes?
Bitcoin nodes only need to work with the state of existing spendable coins.
The need to track previously used stuff in some other systems to prevent transaction replay is a design flaw that Bitcoin avoided.
The vast majority of the blockchain data is digital signatures which you don't need anymore once you've validated them (except to help other people sync up).
