We need to keep in mind that the vacancy rate as we know it applies solely to purpose-built rentals and not rentals made available via investment condos and suites. This is why the vacancy rate has hovered from just above zero to 1.0% over the last decade (we've had no new inventory since the early 1980's save for the last couple of years).
Now over the last couple of years we've started seeing new inventory enter the market, and that has helped the situation to some degree, but it's hard to make an impact with 1,500-units when there are 50,000 purpose-built rentals throughout the region (out of 61,000 total and quite possibly not including suites).
Why we see the "crisis" today is because purpose-built capacity has been constrained for so long that it has now pushed vacancy rates very low even among the least popular tier of housing, that being suites, and the most popular tier (condos made available as rentals) is as popular as ever.
Realistically we're not going to see much reprieve in the official "vacancy rate" until we see 5,000-to-10,000-units enter the market, but we're also facing a situation where upwards of 20,000 existing units will require significant repair or remediation come 2025 so whatever is built today and over the next few years will remain in very high demand.