I agree with pretty well everything you wrote, but this one detail really isn't so.

A fine example of an "append-only" software system is Git, which uses a cryptographically secure "ledger" called a Merkle tree. (Scare quote are because I'm too lazy to deal with all the legitimate quibbles and caveats.)

Corrections are nearly trivial. In the worst case, a legitimately signed "transaction" (commit) was actually by an attacker. To correct, the central authority deauthorizes that key, then creates a new series of transactions/commits starting from the bad transaction with the new key.

I "rewrite history" every day on Git, though we aren't actually signing our commits.

A blockchain contain a Merkle tree, or something equivalent to it, but that's not what makes them pathologically expensive at performing computation.

No, the issue with blockchains is in the consensus stage, where each node in the network has to contain the entire ledger, and then they have to all agree on what the next state of the ledger will be. Suddenly all costs, for memory, CPU, bandwidth or power, are multiplied by three or more orders of magnitude - thousands of times more expensive.

The big con is that this universal anonymous consensus has value beyond the the pervue of "anonymous money for c̶r̶i̶m̶e̶ minimizing government interference" - oh, and wild speculation.