You would lose money attacking the proof of stake Ethereum chain also. Dishonest validators get their ETH slashed.
This of POS as a voting system. currently only 10% of the supply is supporting the transition to POS and end of POW. we probobly will end up with 2 coins. Ethereum POW, Ethereum POS.
What percentage of Bitcoin holders are miners? Probably less than 10%. Not everyone is needed to stake Ethereum to secure the network. In the same way that you don't need 51% of Bitcoin holders to be miners.
There are currently over 300,000 Ethereum validators.