By no stretch of the imagination is Git a centralized ecosystem!

Just because some nodes choose to have an upstream/downstream relationships doesn't make Git centralized, or even those repositories centralized. Upstream and downstream repos don't have to have the same commit IDs at all, for example.

Any Git repository anywhere can have any commit ID, and no repo has all commit IDs. I have repos here that have zero, one, two and three upstreams, and I have repos that are upstreams for other repos.

I can trivially set up N repos, any pair of which share a commit ID, but where no commit is shared by more than two repos, all of which can talk to each other independently.

Git is not centralized.

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I differentiate between "blockchains" and cryptographic ledgers this way - is there a consensus resolution phase like in Bitcoin and other cryptocurrencies? Are there are a large number of massively parallel nodes and a periodic reconciliation phase?

I was sarcastic with the "breakthrough" label but on re-reading, it didn't come through.

The blockchain as laid out in Bitcoin was an advance, though - it provides a heuristic to at least manage a Consensus Problem in a way that's at least verifiable by all parties involved.

You are right that calling it a full "solution" is going too far, but it provides a good enough bodge to build cryptocurrencies in, even though it's a pretty rickety framework.

However, my bigger point still stands - we have had distributed systems for four decades now. If we had wanted to do any of these web3 things before the blockchain, we could have without creating any new magic technology.

The reason we didn't is almost certainly because these ideas just aren't economically viable or even practical (like forcing ticket sellers to accept your cryptographic proof over their own records).

The blockchain's idea of "all nodes contain all information, with a periodic consensus resolution phase" brings nothing to the table for any real-world application except cryptocurrencies, which are "currencies" built on air. (And as you point out, this is a mitigation of the Consensus Problem, not a full solution.)