how about some combination of Merkle trees and HMACs? The person who writes the entry signs it with their private key. No need for PoW miners, a constant internet connection, having nodes compute the head of the blockchain, none of the extra nonsense that blockchains require.
...and then you could group the ledger entries into "blocks" of merkle trees and signing using HMACs, you mean?
You've basically reinvented the "blockchain". The commercially available blockchains are essentially this - they don't use proof-of-work. The enterprise blockchains are not the same as the one that underpins bitcoin.
So where's the innovation? If that's blockchain technology then Linux package managers, PGP, HTTPS and bittorent have been using "blockchain technology" for a long while now. I could've come up with this solution 10 years ago if you had asked me, and I'm really not that clever. Did IBM engineers really just discover public key cryptography?
The current blockchain craze is supposed to find its root in the Bitcoin whitepaper which is about a decentralized distributed trustless immutable ledger. If you remove any of these attributes you end up with something absolutely mundane that definitely doesn't warrant the ridiculous amount of hype, resources and money being poured into it. There are only a very small number of problems that can be solved with a decentralized distributed trustless immutable ledger. That's exactly the point of TFA.
I think this is a very important point to make because many cryptocurrency zealots ofter argue that "the blockchain technology is here to stay, ergo cryptocurrencies is here to stay". Except it turns out that the term became almost meaningless because anything sort of qualifies as a "blockchain" these days, including many centralized systems like IOTA or Ripple or systems that are de-facto centrally managed and mutable (like Ethereum).
If people realize that Blockchain is 90% hype, 9% old technology and 1% actual innovation then maybe they'll think twice about whether having a ~$400 billion market cap for cryptocurrencies is sustainable in the long term.
That's the key problem here, people can't agree on what a blockchain is, and keep re-defining it to meet their implementation needs. If you think decentralization is fundamental you won't accept the enterprise blockchains into the definition, but the B2B companies aren't going to look at it that way.
This is what usually happens when marketing around a term gets too froth (see also, AI).
You're right and I don't want to get too far down the road of defending blockchain (as I seem to have unwittingly done). The marketing most certainly is over the top.