I agree with you there are many complexities and there is no simple equation. My counter argument to your point is that when demand drops, prices come off and young/first home owners are able to enter the market, while this reduces rental property demand, would it not also reduce rental property supply? Thus possibly maintaining a "status quo" with rent prices?
I don't have a real answer, its just that I've often read the other way with regards to the argument for "negative gearing" was a downward pressure on rent as it leaves property owners with less pressure to increase rents even if they are not cash flow positive on an investment property".
