Since when is blockchain a breakthrough? It has not solved any problem, including the Byzantine Consensus problem. That is unsolvable.

I think you have confused your own terms here; a centralised blockchain and a cryptographically signed ledger are the same thing in practical terms, and they are still alterable. You just can't alter them unless you are the central authority. I don't know why you are differentiating between these two phrases.

Git is a centralised ecosystem; how you store data inside such a centralised system isn't really relevant, whether you use a blockchain or anything else. Cryptographically signed ledgers only make it *harder* to alter things - not impossible. A corrupt central authority could alter them by re-computing all of the cryptographic signatures upon changing a block, for example.

One of the core points of this article is that nothing can solve the consensus problem. Even supposedly "secure" PoW blockchains like Bitcoin, which are only "secure" due to the energy they use, are not actually secure; it's actually relatively simple to compromise, it just means having control of a lot of hardware. That's not too difficult given the continued centralisation of wealth (and thus, capability to buy hardware) in a small number of hands.