'it will severely cripple the adoption', I'm not sure it's so straightforward as that, if large numbers of governments take an authoritarian stance on independent global currencies is there not a possibility that, while impacting network efficiency, it might underpin a new found desire and need for said independent global currency and instead drive adoption of currencies that have this resilience?

I think it’s worth than that for bitcoin as bitcoin relies on a connected network for security. The risk of forks is too high without that. For other cryptocurrencies based on BFT at least the network would come to a stop and safety wouldn’t be violated (no double spending).

True, but that failure mode doesn't exploit the network's centralization and is unrelated to how centralized it is.

So it means centralization might not be too relevant to the government a ability to ban.