This is false. At least false for Ethereum's hybrid PoS.
It uses Verifiable Delay Function as an element of random number generation process. One can look into number of rounds of VDF and treat them just the way they treat proof of work today. It can be compared to determine which chain is the longer one.
Chia Coin is working on a VDF ASIC so that they can correct for it in advance (essentially selling it at a loss so everyone can own the best VDF) but I'm not sure it's the same VDF as Ether.
