The top 0.001% don't need to meet in a smokey room to collude. If they have similar enough motivations (remain wealthy) and operating framework (buying power) they can "collude" by simply acting the same way. Most drivers on the road all behave similarly even though they didn't all meet and coordinate ahead of time. They have similar goals and a framework to operate in.

It isn't them though - it is a far narrower group. All blockchains have a rich get richer problem - the earlier you are, the cheaper it is to amass an unassailable position.

Even in something more difficult to collude/setup like BTC, 4 pools could execute a 51% attack. As of Q2 2020, 65.08% of hash power was in China.

It doesn't take many people, especially because you need both money and a desire to be in Ethereum. As another example, 2241 individual wallets hold 42% of all BTC, while 35,604,096 wallets hold 1.24% of BTC - I would expect concentration to happen even more quickly in PoS.

So if all it takes is 4 miners to pull together - and that's never happened - but it would take 70k individuals with Proof of Stake - wouldn't that make it much less likely to happen???

That's only in a fully deployed system. 70k people won't participate in the first buy of PoS ETH - you'll have a far smaller number, likely less that BTC at scale.

Also, ETH has already forked over a doctrinal issue - I don't doubt it could happen again, but the PoS leaders will just directly double down.

This isn't a PoS/PoW argument - more that most public blockchains are inherently winner take all systems.

If someone figures out how to determine the stakes needed to rig up a cheap 51% attack, it breaks the network.