I wish to discuss the following attack vector, as it seems to be a major security risk for Bitcoin.
If Ethereum mounted a successful 51% attack on Bitcoin, it would likely crash the value of Bitcoin, making Ethereum the new number one cryptocurrency.
The cost of a 51% attack has been estimated to be $6–$20 billion [1]. This is only 1.3%–4.4% of Ethereum's current market cap. And it is only 0.5%–1.5% of its potential growth if Ethereum knocks down Bitcoin and conquers its full share of the cryptocurrency market.
The fact is Bitcoin network had biggest total hash rates back in days when Ethereum blockchain was still Proof of Work.
This site gives you some information with its archive through Wayback machine.
https://howmanyconfs.com/Archive in 2020
https://web.archive.org/web/20200814025529/https://howmanyconfs.com/And now Ethereum is no longer pure PoW, how do they attack Bitcoin network by shifting rigs to mine Bitcoin rather than ETH?
A thread on risk of 51% attacks with main content from Jameson Lopp's blog.
How many Bitcoin confirmations is enough?