you haven't thought it through.
what you're talking about is a hard fork.
for starters, good luck getting the node runners or ANY significant part of the Bitcoin network to follow a hard fork. any suggestion that there would be a fork would split the community and crash the price.
so either the attack would succeed because the fork didn't get any support or was irrelevant,
or the attack would fail because there was a fork.
either way the Bitcoin network gets fucked. which I assume is the point of attacking it. I don't think we can assume they're attacking because they want control of the network, maybe they just want it gone.
tldr, there is NOT asymmetrical risk in executing a mining attack.
BUT they dont have to do that and they probably wont.
they just have to write letters to mining companies and threaten them with regulatory burden until they comply.
otoh
there are no mining companies to write letters to on Monero. so the most likely source of mining pressure actually doesn't apply at all.
and if it comes to the nuclear option, monero has already forked twice to arrive at the current mining algo. theres absolutely no reason they can't do it again. AND the project is easier to come to consensus than Bitcoin.
it would still be traumatic for the community no doubt, but less so because they dont rely on institutions anyway.
the main difference is there isn't an ASIC industry ready to go.
this could be a legit problem, in the extremely unlikely scenario that you're talking about.