I absolutely agree on that is a band aid because as you mentioned, the problem is the supply. But it I understand why it doesn't work because we are approaching housing as an investment and not like a right of having a roof over your head
As you mentioned, the top priority would be tackling multiproperty, specially as you point out, investing firms that after 2008, they had been pouring billions and billions in the housing market. Why an entity, firm or individual would need more than 2-3 properties? to make money of it and basically back to capitalism.
Free market is all nice and dandy, but as no one in Europe would discuss a private free market on health care or judiciary system, I don't know how something so basic for security of living like housing has to be left to the free market.