How is Lightning impractical? I encourage you to try it out on testnet right now, it works great. It also solves your PoW concerns.
Maybe you can explain the solution to the problems highlighted?
On top of that LN is very practical for heaviest blockchain users, that do run full node 24/7 anyway.
Like any crypto currency, the numbers in computers are worth whatever people believe they’re worth. So when enough people believe said numbers are worth zero, then the currency will be worth 0. Some may say the same is true for fiat, however the difference with fiat is most national currencies are backed by the might of military force to convince or coerce people into believing the value is > 0.