I challenge #2.
A 51% attack only gives an attacker a chance (a 51% chance, or however much of the hashrate they control) to double spend their own coins, it does not give the attacker any increased ability to change consensus rules.
In fact, changing the consensus rules as a 51% attacker would immediately render your 51% advantage moot, as you would be excluded from the network by the other 49% of participants.
Reason I say it is because the nodes/miners choose what version of Bitcoin they run. So if 51% run a new consensus protocol, that will "force" the chnage, but splinter the network and ruin the network's reputation.
Yea but that's the same as 0.000001% of miners "forcing" a change. They aren't "forcing" anything. There is no "force" in Bitcoin. Only choice. You can chose to run different rules, and it doesn't matter if you control 1% or 50% or 90% of the hashrate. The Bitcoin network will ignore you and proceed undeterred.
No amount of miners trying to force anything will ever make my node accept anything other than. 21M
