How it's better than WebMoney then? About other cryptos - well, yeah, there can be only one. If you don't control 51% of overall humanity hashrate it's not secure (and not better than WebMoney).
Proof of Stake has the advantages that anyone (with sufficient money, or by gathering into pools) can become a validator, and the system itself provides extremely strong incentives not to cheat by slashing their stakes if they do. This slashing weeds out bad actors over time, as well - once their money's gone, they can't stake anymore.
I could imagine all sorts of shenanigans that could cause a small group of companies operating a money system to cheat, either of their own accord, or forced to by a government, organized crime, hackers, etc. Much harder to attack a huge self-healing group of globally distributed validators with extremely strong incentive not to cheat.
All I'm saying that Satoshi really produced the one undeniable cryptocurrency. His idea is sound, you don't need any friends or websites, or "common" knowledge besides his simple idea of the most work burned chain. Anything other is really questionable.