"The proof-of-work also solves the problem of determining representation in majority decision making. If the majority were based on one-IP-address-one-vote, it could be subverted by anyone able to allocate many IPs. Proof-of-work is essentially one-CPU-one-vote. The majority decision is represented by the longest chain, which has the greatest proof-of-work effort invested in it."
Just because one group of devs calls themselves the arbitrators of all things Bitcoin doesn't make it so.
Hash power is relevant to 'regular' forks, as the longest chain that follows the rules will be followed. However hash power is not relevant for deciding what those rules are. That is done by full nodes, whether miners or not, and doesn’t depend on costly work or anything else. Nodes that don’t agree on the rules just stop talking to each other, and the network splits.
Then, the final decision about which network and chain trades as “BTC” is made by ordinary real world consensus, probably mainly among exchanges, wallets, and users in general.
Edit: Changed 'soft fork' to 'regular fork' because a soft fork is a protocol change. POW chain-following doesn't even rise to that level.
For Bitcoin, the difficulty adjustment would also need to be sped up, to keep the minority chain from being very slow for a while.
To be clear, I'm not saying 2X is itself an attack (IMO, awfully close to crossing the line, though). I'm assuming that in your scenario, some mining faction is spending part of its compute on running 2X, and part on explicitly 51% attacking the original network.