The LCR insures no double-spend exist.
Once quantum computers hit the market everyone will be able to rewrite complete Bitcoin blockchain from the genesis. So I would add something to emphasize temporal nature of your statement.
This is also the benefit of an append only ledger and an issue with POW.
Even a quantum computer cant rewrite history in a ledger that is append only. Sure it might be able to disrupt future transactions if sufficient algorithms are not in place to account for quantum computing resources, but the fact still holds that the past data prior to any quantum influence is sound and can be trusted.
Also, I haven't looked into how a QC would do this, but how would it get around the Bitcoin checkpoints? Surely it can only rewrite from the last checkpoint issued?