For others you gotta research the etherem's smart contract protocol and the flaws it has, like the most famous one that led to DAO issue and the subsequent roll back. A flaw that was never fixed.
It's not a 'flaw' it's a feature. Smart contracts don't stop you from doing anything stupid, that's not their job. Look at the thousands and thousands of token scams that keep popping up on ETH.
People are still sending their ETH to contracts that will do nothing but take their money.
...It's worth noting that in that discussion, it was pointed out that only two companies control more that 51% of the Bitcoin hashrate. An entity controlling these two companies (either through legal/political or clandestine means) could effectively control the Bitcoin network....
Pools are not miners. I am guessing that you are taking about Foundry USA and AntPool
Although they do host some miners that are under their control a lot of the mining hashpower that is coming into them is from independent miners running their own equipment. As soon as it looks like they are doing something funky / non legit people are going to point their miners elsewhere. If they get too big people will point their miners elsewhere. Even going back 10 years ago (crap has it been that long) GHash.io hit over 51% and the community freaked and miners moved off. It was a minor worry then and an even smaller one now.
-Dave