I don't think immigration is the issue since that actually helps fuel the economy,
"Fuelling the economy" doesn't mean more houses get built proportional to increases in population. It doesn't mean every immigrant generates enough economic value to make construction of an additional housing unit economically feasible. And let's not even begin to discuss the impact on physical and social infrastructure more broadly.....
No, higher prices encourage supply. Investors and developers don't stand at the sydney airport arrivals lounge with a clipboard counting how many people are getting off the plane.
But housing is strongly supply limited. Material and construction costs have risen sharply, building companies are failing, there's a shortage of workers (not least because the unions conspire with labor to keep migrant workers out of the constuction industry while creating more demand for construction jobs through population growth) and so on. The issue is not and cannot possibly be a lack of demand. And of course, the issue is a lack of supply
relative to the number of people. If immigrants do 'encourage supply', this cannot possibly make things better unless they magically encourage supply to increase to a greater extent than the population increases, but this simply isn't happening.
If what you are saying were true, there wouldn't be 100 people queuing up around the block for every rental viewing in sydney. There simply aren't enough houses compared to people, it's getting worse every year, and there's no magic fix for it. Things clearly aren't keeping up with the current population size, but the population is continuing to grow every year.
but I'd say foreign investors and CGT/etc definitely distort the market a bit, somewhat offset by banks charging higher interest rates for investors (but that really only impacts people borrowing money from an Australian bank which I suspect at least some of the foreign investors aren't).
CGT can't explain why there's a shortage of places to rent unless investors are deliberately choosing to leave properties vacant long term instead of renting them out at significant numbers, which is unlikely. And of course, everyone is already blaming domestic property investors while screeching about "racism" if you so much as mention 'foreign investors'.