My understanding is that the danger of miner control is not "double-spending" but making multiple spends and being able to pick the most favorable one after the fact.
As a non-controller if you try to double-spend, you can't know which one of your attempted transactions will be recorded in the ledger and which will be rejected. As a 51% controlling miner, you can choose the 'correct' transaction.
This allows the 51% controlling miner to engage in futures arbitrage.
If it wasn't clear, my comment was referring to a double-spend that would result in an invalid block i.e. both transactions are on the same chain. I simply used an example to argue that it's always been the case that invalid chains are rejected by honest nodes.