The difference between the UK and Australia is Australia has tight controls on foreign property ownership, and it can be quite a hassle to buy if you're not a long-term visa holder or citizen. Long-term visa holders also have to sell the property at the end of their stay.[0] Australia also has a decent number of moderate-stay (<=12 months) temporary residents (working holiday, etc) that aren't allowed to buy under FIRB guidelines, or don't have the fiscal means, both of which increase demand for rentals.
I strongly doubt whether the increasing price of housing is sustainable. If it's increasing beyond that of inflation, it's a bubble and people simply just aren't going to be able to afford it. People on the upswing of any market become complacent that prices will always continue to rise, but this isn't necessarily true. The future is yet to be determined, and who knows what will happen.
I have known landlords who have had their properties vacant for several months at a time. Their mortgages continued though and this put a lot of pressure on them financially. There's also the issue of tenants that end up not paying, or paying late, etc.
You're not wrong and your strategy has a strong superficial appeal: property ownership with flexibility! Properties can be rented out, it's possible to find great long-term tenants, and it's even possible to break even or make a slight profit as an amateur landlord. Your strategy can be made to work, it's just the costs probably aren't worth it unless you're a landlord with a good number of properties. I'd argue the actual flexibility is marginal compared to renting; if I want to leave my rented property, I can do so quite easily and with minimal moving costs. I do appreciate the cost of this flexibility too though: I'm paying someone else's mortgage with nothing to show for it in the long term. Also, owning has the distinct advantage of control: nobody's going to be a more accommodating landlord to me than me!
[0] This assumes that the property is a second-hand dwelling, not one bought from a new developer, or been renovated, or any of the other exceptions that come to mind.