That is true only to the extent that proof of work has already been performed. You have to stake something of value or POS doesn’t work. Staking a POW coin to “mine” a new POS coin works. So does burning a POW coin to convert it to a new POS coin that can be staked for more. But, you can’t bootstrap a POS coin without leveraging proven investment from previously burned work.

At this point Bitcoin and Eth have about a trillion USD of built up burned work. Is that enough to prime the pump for a POS-based world economy? I dunno. Probably?