> If I and my grandma and everyone's grandma would use Proof of Work cryptocurrencies to buy peanuts at the supermarket

Beyond your misconception that work scales with users rather than value, it's also a misconception that bitcoin is competing with technologies like Visa and Paypal. It's not supposed to be an alternative payment system.

It's competing with gold and sovereign currencies.

Your grandma won't ever use it directly.

Your government might.