Blockchains efficient? They are not compared to the databases banks are using now. Blockchains are slow, use too much storage and bandwidth. Also a real blockchain uses Proof of Work which is considered wasteful in the use energy by most people who do not get that it is actually a breakthrough.
We will soon see all these private "blockchain" pitches by different developers to pivot into something else and drop the word "blockchain".
your thinking of bitcoins blockchain. trying to fit bitcoins concept into the banking industry..
wipe your mind of bitcoin and concentrate on underlying blockchain, again without thinking about all the unique bits that separates bitcoin from the other altcoins.
like going back to the design board and opening your mind to design your very own altcoin.
it doesnt need to be all data on every node(bitcoin) or all data on one server(banking).. it can be inbetween aswell
EG a texas sidechain where all the banks in texas reinforced each other. california have a different sidechain where all the banks in california reinforced each other
imagine each block is not hashed by PoW with a 10 minute target. but instead signed by xx regional hubs/bank branches in a split second.
imagine it like live data is instantly signed off as soon as its altered. and this continues on for a month. then at the end of the month. its locked for good, as historirc record. and then a new block copy is opened up to then change live. like a monthly statement of locked historic blocks and a live block ontop that is the 'current balance block'
making the live active block (much like mempool/LN) editable until its locked. but trusted available balance due to instant multisig signing
imaging instead of one central server hosting every bank account data, there was instead a bank branch that had its own account holders (sidechain) where they all inter-communicate between sidechains, like the same way routing numbers /sort codes recognise which HQ server to address for particular banking customers. but this time the data is distributed into hubs/regions/clusters/sidechains.
once you wipe your mind of bitcoin and see how loose the term blockchain is. you realise blockchain alone is just an empty tool. but is a tool that can do some very funky and unthought about things