Ethereum founder VItalik Buterin stated in Twitter that since 2014, PoW has not been more equal than PoS. The 51% attack on PoS is not irrecoverable, because it can be solved using the method of user-activated soft fork (UASF). The security of PoS is an inductive argument and is completely reasonable. In addition, PoS and PoW have different resource consumption. PoW requires permanent investment. The life of PoW ASIC is only about 2 years and the operating cost is high, while PoS is closer to pure capital expenditure.