The main point the author is making is that PoS doesn’t require spending of any scarce resource on a per block level so the accuracy of the distributed clock is not to be trusted. I don't think they misunderstand their argument. You’re just not replying to it.
You spend "safety of your stacked money while having stacked a lot of money" it's a scarce resource as if you over spend it you lose your money. And the more money you have stacked the less interest you have into braking the currency as it makes you lose that money.
