The fundamental truth here is that wealth is finite.
This is flatly false. I don’t actually know of any economist that believes this; even the Austrians, let alone Keynesians. The amount of wealth is not a static ‘pie’ that we are all taking a slice of. That doesn’t even fit the neoclassical model.
Unemployed labor is a huge cost; potential ‘wealth’ that does not exist. The same is true of underutilized real assets. Why else does financial stimulus boost the economy and increase wealth? You cited Paul Krugman earlier and are now denying even mainstream Keynesian economics