Then you fail to understand the incentive structure. The only game-theory outcome to a PoS system is a monopoly. That's the reason why there aren't any successful ones. Because they require trust.
Agree, I fail to understand what you mean. If I'm a large owner of a POS coin, why would I want to steal smaller owners' coins ? Don't I want them to trust the system and keep buying more coins ?
Elaborate? I mean mining pools in China with the oligopoly bit. Are you saying that's not a problem? I would say the current bitcoin PoW scheme is inherently seeking to end up in a few actors having most of the power due to the higher and higher barriers of entry to mining on custom silicon. ELI5 why I'm wrong?
Nodes define and police consensus in bitcoin, not miners. Miners have a single choice : mine for bitcoin according to node consensus rules, or don't. That is the only power they have.
in theory. But in practice, if tomorrow fork XYZ comes out and miners decide to mine that fork, instead of the current one, the current one is finished. So, don't they hold all the power in practice ?
No. You completely don't get how it works. Only by mining according to bitcoin consensus rules do they get bitcoin rewards. Their fork relies upon you using their node client in order to give them tokens. If nodes don't switch clients, no one even knows the fork exists.
This entire episode over the past year has demonstrated this again and again. Miners talk a big game, but in the end, they do as they're told.