I think their plan is: Increase supply of (actual) starter and family homes that have been lacking -> these homes are sold at low prices and start dragging the rest of the housing market lower -> government chops interest rates and increases loan guarantees and incentives as much as needed to prevent prices of other homes from falling
All of these actions will help improve housing affordability and make homeownership more accessible, but not all of them will lower prices, some of them cause price inflation. I think he's intending to balance these to keep the market neutral. Whether they can successfully pull that off, remains to be seen. But Carney's not stupid, he knows he can't tank the housing market. There are literally millions of Canadians depending on the value of their house, for better or worse, it may be a bad and stupid situation but we're deep in it now and Carney's not going to rip the bandaid off yet. His goal will be to stop it from getting too much worse and try to keep it stagnant for a long time so that incomes and economics get a chance to catch up.
Yes it would be nice if you just got a reasonably priced house right out of the gate and didn't have to take out a low interest mortgage to cover the unreasonable additional cost. But we're not there yet, and I think Carney's plan is going to take that into account.
We'll see if I'm right. This is all speculation.