...Yes, it would take some time if the Ethereum stakeholders choose to set up the farms themselves, but it can be be done, even if it will take several months....
YEARS not months. That much excess mining gear does not exist, so you would have to have been stockpiling for at least a year if not 2 or 3 to get that amount of gear. Or you could just take over the used markets and buy it all but then you are suffering from having an mixed batch of used equipment you have to deal with.
Fair enough, let's agree to assume that it could take years (i.e. given that the existing Bitcoin miners are somehow very loyal and cannot be bought by the competitors/attackers).
So, do you really thing while someone is buying billions and billions of dollars of mining gear over a couple of years (and not mining with it) nobody is going to notice.
Remember, other people will keep buying gear and increasing difficulty and that would make you have to buy even more gear (and not mine with it) otherwise you will be driving up the difficulty on yourself.
ETH being a POS coin with as I stated above 60% of it's capacity at 3 providers would be easier and cheaper to kill. Think about it $20 billion will get you 1% of Amazon stock and a complete buyout of Hetzner & OVH
With 1% control of the Amazon stock it would be simple to put a proposal out to the board an have them shut down all ETH nodes hosted there along with the others you could take out 60% of the ETH nodes leaving people hanging. And then watch as a bunch of the remaining stakers all start to sell to get their coins out before the total crash.
Could probably do it for a lot less Hetzner has 18% of all ETH nodes out there and the company is valued at less then $3 billion OVH has 12% of the nodes and it valued at a lot less add in a couple of others for for $5 billion you could control over 35% of the ETH nodes and close to 50% of the staked nodes. Then you come in one morning and shut them all off. Sit back and watch the chaos.
Most people staking have no idea what to do or how it works, all the know is they clicked a few keys and now their ETH is earning less then having sold it for cash and putting that cash in a savings account. (3.25% give or take for ETH vs 4%+ for a good savings account and if you want to lock up your cash like the ETH stake people have their ETH locked up you can get 5%+ on a short term CD)
If someone (or some government) wanted to attack
BTC there are better / cheaper ways of doing it then mining. EVERYONE knows this more or less. And as I keep pointing out since no person / government has done it it just kind of proves that they know that even if massively attacked
BTC would improvise & adapt & overcome.
-Dave