Relative scarcity is the necessary and sufficient condition. Either there's enough housing or there isn't (there's a bit of slack with relocations, house sharing and spare bedrooms but it's largely inconsequential.) That means that supply (i.e. quantity) is enough.
It's true that if it was impossible to speculate on housing, there would be less incentive to create artificial scarcity by e.g. lobbying for restrictive land use policies.
It's true that if it was impossible to speculate on housing, there would be less incentive to create artificial scarcity by e.g. lobbying for restrictive land use policies.