You neglect the part of the scheme above that's moronic because you spent tens of millions of dollars to attack a chain with less than that much immediate liquidity on any exchange. If you were to spend tens of millions of dollars making lots of ASICs, why not just mine with them like everyone who has made ASICs so far is doing?
If you attack it because you're a state actor who wants to get people to use your fiat money instead of leaving it for cryptocurrency, the liquidity on the exchange is irrelevant.