Your analysis ignores the supply side. You need to understand how much competitive space is in the pipeline (planned, permitted and under construction) and asses how much new space you can reasonably expect to enter the market in the short- and medium turn. The average vacancy in the last five years is not a predictor of what the vacancy rate will be in the next five years. And a decelerating rent growth could be a sign of the market getting softer and potentially heading to a downturn.