How about instead of using some hypothetical situation that has nothing to do with reality, why not instead figure out how things actually work now and go from there?
The reality is that there are anti-BTC entities. There are also big miners. At the right price, big miners may sell their mining hardware to anti-btc entities.
You had mentioned an entity that owns lots of mining hardware. I agree that is a problem.
Suppose there are multiple such entities now, BTC will be in trouble.