The issue here is that demand shifts regionally over time. Dwelling units in Detroit don't satisfy demand in San Francisco. The result is that you continually have to increase supply in the places demand currently is. To keep prices flat, the number of units per thousand inhabitants has to increase over time, because the number of empty units in areas that have fallen out of demand will increase, but the high prices you're trying to avoid will be somewhere else.
> By definition, only investment properties can be underutilised - owner occupied homes are occupied!
This is also not true. You can have e.g. a 3-bedroom home with one occupant, even if the occupant is the owner. You can also certainly have underutilized land -- any single family home in an area where there is demand for more housing but zoning prevents it from being constructed on that piece of land. Because then you have that acre of land providing housing for one family when it could have been two or twenty.
> global asset price inflation driven by a broken financial system (i.e. a system being artificially pumped up with cheap credit).
This can only happen when supply is artificially constrained. If it cost $200,000 to add a housing unit and suddenly everyone can get a bigger loan than before, the instantaneous effect would be for housing prices to increase -- but once they're above the construction cost, construction occurs until they no longer are, i.e. until they fall back below $200,000.
At that point cheap credit might cause people to buy bigger houses, or use the loan money to buy things other than housing, but long-term you can't get the price of the same housing unit to increase above the cost of creating more of them, or supply would just increase until it fell back to that cost.
What you can do is increase the cost of creating supply, e.g. by restricting where it can be done, so that the cost of doing it goes up and with it the price of a given housing unit. Which is what has happened.
