I don’t get this argument that lack of anonymity is a fatal flaw when various effective anonymizing solutions exist.

It’s only not a flaw if people do take those extra steps. By default, it’s not anonymous and that is an important caveat.

It’s an objective fact that cryptocurrency is massively more resistant to civil forfeiture than physical cash.

As is a bank account if that’s the threat model. Everything is relative to a threat model you want to protect from.