Thanks for the informative post. Great info. As for your question...
No way. Bitcoin can not be 51% attacked. By design, if any group gets enough hash power to 51% attack bitcoin, it is far more lucrative to just mine it. Fully incentiveized to play by the rules.
That is a moot point anyway because bitcoin is the most powerful computer the world has ever seen. A consortium of nation-states and banks computing power combined cannot 51% attack bitcoin.
Most altcoins are so vulnerable because there are very few nodes running and very little hashpower protecting them. Most altcoins don't consider security.
That's why Antonopolous predicted this would happen back in 2014. And he was right. This is just the beginning.
Fear not. Bitcoin is completely invulnerable. Literally can not be stopped.
Thanks for the reply. I think we'll see more altcoins and other blockchains hash into BTC for its security.