Yeah I think that view complements what I've said. I was controlling for market cap, but you're absolutely correct that if we view the security budget as fiat market cap as currently its valued at in both blockchains, any fiat price dump nukes the hashrate for both.
Though, this is just a free market force, most will mine for a slight profit, and little to nobody will mine for a loss such that if mining rewards become less than electricity, you just consequently find less miners.
Maybe one day we will have true price discovery and equivalent security to match, but for now it's really tied to market cap unfortunately.