But also any transactions pertaining to a "dead" account has to be verified whenever a new node boots the chain from scratch, in all future. The aggregated cost in power will, in time, surpass the initial cost of buying those coins.
I don't think so, though maybe I am misunderstanding. In the pathological case, imagine that a node has made no transactions at all for a year. The owner will have to go to look up how much money they have in the ledger before they can complete a transaction and discover they have no money. The space complexity of maintaining accounts is extremely small compared to maintaining transactions. All transactions that were associated with that account have been wiped from the public ledger. An archival ledger may keep a record of retired transactions, but the archival is not required to settle all accounts.
But that assumes that there is a trusted archival party that can verify account balances with authority. It may be technically possible to devise such a system, but as far as I understand, current decentralized blockchains require that you replay all previous transactions in order to learn the current state of the system.
I'm new to blockchains so I'm sorry if this is stupid, maybe somebody can explain to me.
Why do everybody needs to keep everything? The chain will be much smaller with just the id and the hash of the block. The payloads could be kept only by the interested parties and could be validated when needed with the chain.
Because every node in the network must be able to verify all transactions all the way from the genesis block. In order to ensure that this is possible, everyone who keeps the history must keep the full history.
With the MimbleWimble design [1] [2], inputs may be cancelled against the outputs they spend, with no loss of security. Essentially, the entire blockchain history may be collapsed to a single mega transaction, with all coinbases as inputs and the UTXO set as outputs.