I favour the theory that the majority of inhabitable planets are yet to be formed/reached that point of their existence. I think it was estimated that about 90% of the planets likely to be inhabitable at some point are yet to have reached that point.
So, we're like the alpha model intelligent lifeform (or at least, there are less than expected lifeforms at this particular point in time).
Still...I don't see a slam dunk answer (which is fine) hence my comment about 'easy'. Equally, though, your points are valid, and uncomplicated, so in that sense you are completely correct.