We need Ethereum to always prevent this. Or the big mining pool will just do this for every block and allow ONLY THEIR blocks to be processed. Then they get 100

We need Ethereum to always prevent this. Or the big mining pool will just do this for every block and allow ONLY THEIR blocks to be processed. Then they get 100% of mining of the ETH mining fees. This reinforces by most miners being willing to join, to get a share in monopoly rents over miners-never-earning. The big mining pool(s) could let in enough to stay big enough. But not too many to spread the monopolistic gains by too broad a base.