I’d say that Marxism at least is fatally flawed. The idea that you start a Communist society by gathering all power to a central council is the issue. Once power is obtained it’s never willingly dispersed. This has been the fate of existing all communist governments

Which system IS stable? AFAICT every system ever has allowed some people more power than others and those people cleave more power to themselves over time. This appears to be how most empires fall

Pumped hydro? Or one of the many other non battery storage options, or just over production