"Any approach that focuses on just one side of the equation is wrong."

That is a false premise.

There is nothing wrong with placing more emphasis, focus and policy change on the CAUSATIVE side of the equation. 

The CAUSE of the problem is external money (not earned by locally employed workers). That EXTERNAL MONEY is the ONLY way to get house prices to dozens of times the average annual local income. It is the ONLY way.

And that is where your false premise falls apart. A limited supply alone in a Canadian city CANNOT get house prices to dozens of times the average annual local income. It is an economic and mathematical impossibility. Banks do not give to young workers a bunch of mortgages for dozens of times their annual local incomes.

That is why you MUST first and foremost address the causative side of the equation, which is the DEMAND side. And the massive, buckets-of-dollars-from-the-sky demand is coming from the noted EXTERNAL source.